Touch sensor detector system and method

ABSTRACT

A touch sensor detector system and method incorporating an interpolated sensor array is disclosed. The system and method utilize a touch sensor array (TSA) configured to detect proximity/contact/pressure (PCP) via a variable impedance array (VIA) electrically coupling interlinked impedance columns (IIC) coupled to an array column driver (ACD), and interlinked impedance rows (IIR) coupled to an array row sensor (ARS). The ACD is configured to select the IIC based on a column switching register (CSR) and electrically drive the IIC using a column driving source (CDS). The VIA conveys current from the driven IIC to the IIC sensed by the ARS. The ARS selects the IIR within the TSA and electrically senses the IIR state based on a row switching register (RSR). Interpolation of ARS sensed current/voltage allows accurate detection of TSA PCP and/or spatial location.

CROSS REFERENCE TO RELATED APPLICATIONS Continuation Patent Application

This is a continuation patent application of and incorporates byreference United States Utility Patent Application for TOUCH SENSORDETECTOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and JohnAaron Zarraga, filed electronically with the USPTO on Jun. 30, 2021,with Ser. No. 17/363,659, EFSID 43121872, confirmation number 5161,issued as U.S. Pat. No. 11,520,454 on Dec. 6, 2022.

This application claims benefit under 35 U.S.C. § 120 and incorporatesby reference United States Utility Patent Application for TOUCH SENSORDETECTOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and JohnAaron Zarraga, filed electronically with the USPTO on Jun. 30, 2021,with Ser. No. 17/363,659, EFSID 43121872, confirmation number 5161,issued as U.S. Pat. No. 11,520,454 on Dec. 6, 2022.

This is a continuation patent application of and incorporates byreference United States Utility Patent Application for TOUCH SENSORDETECTOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and JohnAaron Zarraga, filed electronically with the USPTO on Dec. 2, 2019, withSer. No. 16/700,325, EFSID 37899441, confirmation number 7975, issued asU.S. Pat. No. 11,068,118 on Jul. 20, 2021.

This application claims benefit under 35 U.S.C. § 120 and incorporatesby reference United States Utility Patent Application for TOUCH SENSORDETECTOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and JohnAaron Zarraga, filed electronically with the USPTO on Dec. 2, 2019, withSer. No. 16/700,325, EFSID 37899441, confirmation number 7975, issued asU.S. Pat. No. 11,068,118 on Jul. 20, 2021.

This is a continuation patent application of and incorporates byreference United States Utility Patent Application for TOUCH SENSORDETECTOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and JohnAaron Zarraga, filed electronically with the USPTO on Sep. 10, 2018,with Ser. No. 16/127,143, EFSID 36897466, confirmation number 1023,issued as U.S. Patent 10,534,478 on 01/14/2020.

This application claims benefit under 35 U.S.C. § 120 and incorporatesby reference United States Utility Patent Application for TOUCH SENSORDETECTOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and JohnAaron Zarraga, filed electronically with the USPTO on Sep. 10, 2018,with Ser. No. 16/127,143, EFSID 36897466, confirmation number 1023,issued as U.S. Pat. No. 10,534,478 on Jan. 14, 2020.

This is a continuation patent application of and incorporates byreference United States Utility Patent Application for TOUCH SENSORDETECTOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and JohnAaron Zarraga, filed electronically with the USPTO on Jul. 19, 2017,with Ser. No. 15/653,856, EFSID 29823046, confirmation number 8397,issued as U.S. Pat. No. 10,073,565 on Sep. 11, 2018.

This application claims benefit under 35 U.S.C. § 120 and incorporatesby reference United States Utility Patent Application for TOUCH SENSORDETECTOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and JohnAaron Zarraga, filed electronically with the USPTO on Jul. 19, 2017,with Ser. No. 15/653,856, EFSID 29823046, confirmation number 8397,issued as U.S. Pat. No. 10,073,565 on Sep. 11, 2018.

This is a continuation patent application of and incorporates byreference United States Utility Patent Application for DIAMOND PATTERNEDTOUCH SENSOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg andJohn Aaron Zarraga, filed electronically with the USPTO on Sep. 21,2016, with Ser. No. 15/271,953, EFSID 26993117, confirmation number2871, issued as U.S. Pat. No. 9,746,964 on Aug. 29, 2017.

This application claims benefit under 35 U.S.C. § 120 and incorporatesby reference United States Utility Patent Application for DIAMONDPATTERNED TOUCH SENSOR SYSTEM AND METHOD by inventors Ilya DanielRosenberg and John Aaron Zarraga, filed electronically with the USPTO onSep. 21, 2016, with Ser. No. 15/271,953, EFSID 26993117, confirmationnumber 2871, issued as U.S. Pat. No. 9,746,964 on Aug. 29, 2017.

This is a continuation patent application of and incorporates byreference United States Utility Patent Application for CAPACITIVE TOUCHSENSOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and JohnAaron Zarraga, filed electronically with the USPTO on Sep. 27, 2014,with Ser. No. 14/499,090, EFSID 20263634, confirmation number 8881,issued as U.S. Pat. No. 9,459,746 on Oct. 4, 2016.

This application claims benefit under 35 U.S.C. § 120 and incorporatesby reference United States Utility Patent Application for CAPACITIVETOUCH SENSOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg andJohn Aaron Zarraga, filed electronically with the USPTO on Sep. 27,2014, with Ser. No. 14/499,090, EFSID 20263634, confirmation number8881, issued as U.S. Pat. No. 9,459,746 on Oct. 4, 2016.

This is a continuation patent application of and incorporates byreference United States Utility Patent Application for RESISTIVE TOUCHSENSOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and JohnAaron Zarraga, filed electronically with the USPTO on Sep. 26, 2014,with Ser. No. 14/499,001, EFSID 20262520, confirmation number 8298,issued as U.S. Pat. No. 9,465,477 on Oct. 11, 2016.

This application claims benefit under 35 U.S.C. § 120 and incorporatesby reference United States Utility Patent Application for RESISTIVETOUCH SENSOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg andJohn Aaron Zarraga, filed electronically with the USPTO on Sep. 26,2014, with Ser. No. 14/499,001, EFSID 20262520, confirmation number8298, issued as U.S. Pat. No. 9,465,477 on Oct. 11, 2016.

Utility Patent Applications

United States Utility Patent Application for DIAMOND PATTERNED TOUCHSENSOR SYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and JohnAaron Zarraga, filed electronically with the USPTO on Sep. 21, 2016,with Ser. No. 15/271,953, EFSID 26993117, confirmation number 2871,claims benefit under 35 U.S.C. § 120 and incorporates by referenceUnited States Utility Patent Application for TOUCH SENSOR DETECTORSYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and John AaronZarraga, filed electronically with the USPTO on Jun. 25, 2014, with Ser.No. 14/314,662, EFSID 19410170, confirmation number 8306, issued as U.S.Pat. No. 9,001,082 on Apr. 7, 2015.

United States Utility Patent Application for CAPACITIVE TOUCH SENSORSYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and John AaronZarraga, filed electronically with the USPTO on Sep. 27, 2014, with Ser.No. 14/499,090, EFSID 20263634, confirmation number 8881, claims benefitunder 35 U.S.C. § 120 and incorporates by reference United StatesUtility Patent Application for TOUCH SENSOR DETECTOR SYSTEM AND METHODby inventors Ilya Daniel Rosenberg and John Aaron Zarraga, filedelectronically with the USPTO on Jun. 25, 2014, with Ser. No.14/314,662, EFSID 19410170, confirmation number 8306, issued as U.S.Pat. No. 9,001,082 on Apr. 7, 2015.

United States Utility Patent Application for RESISTIVE TOUCH SENSORSYSTEM AND METHOD by inventors Ilya Daniel Rosenberg and John AaronZarraga, filed electronically with the USPTO on Sep. 26, 2014, with Ser.No. 14/499,001, EFSID 20262520, confirmation number 8298, claims benefitunder 35 U.S.C. § 120 and incorporates by reference United StatesUtility Patent Application for TOUCH SENSOR DETECTOR SYSTEM AND METHODby inventors Ilya Daniel Rosenberg and John Aaron Zarraga, filedelectronically with the USPTO on Jun. 25, 2014, with Ser. No.14/314,662, EFSID 19410170, confirmation number 8306, issued as U.S.Pat. No. 9,001,082 on Apr. 7, 2015.

Provisional Patent Applications

U.S. Utility Patent Application for TOUCH SENSOR DETECTOR SYSTEM ANDMETHOD by inventors Ilya Daniel Rosenberg and John Aaron Zarraga withSer. No. 14/314,662 that was filed electronically with the USPTO on Jun.25, 2014 claims priority to U.S. Provisional Patent Application forINTERPOLATING FORCE SENSING ARRAY by inventors Ilya Daniel Rosenberg andJohn Aaron Zarraga with Ser. No. 61/883,597, filed electronically withthe USPTO on Sep. 27, 2013.

U.S. Utility Patent Application for TOUCH SENSOR DETECTOR SYSTEM ANDMETHOD by inventors Ilya Daniel Rosenberg and John Aaron Zarraga withSer. No. 14/314,662 that was filed electronically with the USPTO on Jun.25, 2014 claims priority to U.S. Provisional Patent Application forINTERPOLATING FORCE SENSING ARRAY by inventors Ilya Daniel Rosenberg andJohn Aaron Zarraga with Ser. No. 61/928,269, filed electronically withthe USPTO on Jan. 16, 2014.

U.S. Utility Patent Application for CAPACITIVE TOUCH SENSOR SYSTEM ANDMETHOD by inventors Ilya Daniel Rosenberg and John Aaron Zarraga withSer. No. 14/499,090 that was filed electronically with the USPTO on Sep.27, 2014 claims priority to U.S. Provisional Patent Application forTACTILE TOUCH SENSOR SYSTEM AND METHOD by inventors Ilya DanielRosenberg and John Aaron Zarraga with Ser. No. 62/025,589, filedelectronically with the USPTO on Jul. 17, 2014.

RESISTIVE TOUCH SENSOR SYSTEM AND METHOD by inventors Ilya DanielRosenberg and John Aaron Zarraga, filed electronically with the USPTO onSep. 26, 2014, with Ser. No. 14/499,001 that was filed electronicallywith the USPTO on Sep. 26, 2014 claims priority to U.S. ProvisionalPatent Application for TACTILE TOUCH SENSOR SYSTEM AND METHOD byinventors Ilya Daniel Rosenberg and John Aaron Zarraga with Ser. No.62/025,589, filed electronically with the USPTO on Jul. 17, 2014.

PARTIAL WAIVER OF COPYRIGHT

All of the material in this patent application is subject to copyrightprotection under the copyright laws of the United States and of othercountries. As of the first effective filing date of the presentapplication, this material is protected as unpublished material.

However, permission to copy this material is hereby granted to theextent that the copyright owner has no objection to the facsimilereproduction by anyone of the patent documentation or patent disclosure,as it appears in the United States Patent and Trademark Office patentfile or records, but otherwise reserves all copyright rights whatsoever.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO A MICROFICHE APPENDIX

Not Applicable

FIELD OF THE INVENTION

The present invention generally relates to systems and methods in thefield of touch sensor devices. Specific invention embodiments may haveparticular applicability to touch-based force-sensing devices andmethods for determining the location and amount of force exerted on apressure-sensitive surface.

PRIOR ART AND BACKGROUND OF THE INVENTION

In the field of touch-based force-sensing apparatus, multi-touch sensorshave been developed and are commonly used to add touch-based user inputto a variety of communications and computing appliances includingcomputers, tablets, and similar electronics devices.

Multiple touch pressure or force-sensing relative to a force-sensingapparatus refers to the ability of a computing system using touch-basedsensors to distinguish and independently track multiple touches exertedin real-time against the sensing apparatus. Such technology enablescomputing appliance operators to use multiple hands and fingers andother objects such as a styli to provide input and enables multipleusers to simultaneously interact with the sensor apparatus.

One problem with existing touch sensing systems is a requirement foraccuracy in determining the precise location and nature of the forceexerted against the sensing surface. Moreover, there is a market demandfor larger devices having larger touch-screen areas for enteringtouch-based instruction to operate computing programs and applications.There is also a need for small sensors (such as touch sensors for mobiledevices) with improved tracking resolution. Therefore, there ismotivation in the art to seek touch-sensing technologies that remainaccurate and may still be economically feasible for manufacture andoperation.

Therefore, what is clearly needed is a force-sensing apparatus that canbe provided in a larger footprint with less electronics and that maysense the presence and location of, as well as the amount of forceexerted with every touch in a multi-touch sequence of input operation.

Background Information

One of the greatest challenges in creating a multi-touch sensor for userinterface applications is that most people are capable of extremelyprecise movements, and expect the touch sensor to faithfully capturetheir input. For a good user experience, a touch panel for fingerinteraction usually requires accuracy on the order of 0.5 mm, whileinteraction with a stylus requires even higher accuracy on the order of0.1 mm. Furthermore, most users want larger device surfaces to interactwith. This is evidenced by the increasing sizes of smart-phones, and thegrowing popularity of devices with larger touch surfaces such as tabletcomputers and touch displays.

Furthermore, the complexity of consumer electronic devices tends toincrease over time while prices tend to decrease, which suggests thatany touch sensor device used for consumer electronics applications mustbe inexpensive to manufacture and must have a high performance to priceratio. Thus, a sensor that can track touches very precisely over a largearea, and can be manufactured at a reasonable price point is needed.Finally, users want extra dimensions of interactivity. This technologyprovides not only precise touch tracking over large surfaces at areasonable price point, but also measures the extra dimension of forcefor every touch, which can increase the level of interactivity andcontrol in many user interface applications.

Deficiencies in the Prior Art

The prior art as detailed above suffers from the following deficiencies:

-   -   Prior art sensor systems require individual column drive and row        sense circuitry for each row/column in the sensing array.    -   Prior art sensor systems consume significant dynamic power in        scanning the sense array because each column must be driven and        each row sensed to detect pressure/presence at a given        column/row intersection in the sensing array.    -   Prior art sensor systems require significant electronics        integration to support large area sensing surfaces.    -   Prior art sensor systems are not capable of sensing contact and        pressure with the same device.    -   Prior art sensor systems require relatively complex        manufacturing processes to achieve high spatial sensing        resolutions.    -   Prior art sensor systems are generally not compatible with        standard PCB manufacturing processes and methods.    -   Prior art sensor systems are not amenable to construction in        non-planar formats.    -   Prior art sensor systems require relatively complex calibration        procedures to achieve accurate sensor positioning data.    -   Prior art sensor systems do not produce a linear relationship        between sensor data and detected spatial positioning within the        array.    -   Prior art sensor systems are not conducive to the design of        non-rectangular sensor shapes due to non-linearity which results        when creating a non-rectangular sensor.    -   Prior art sensor systems do not allow scanning the sensor at        various resolutions while maintaining linearity.

While some of the prior art may teach some solutions to several of theseproblems, the core deficiencies in the prior art systems have not beenaddressed.

OBJECTIVES OF THE INVENTION

Accordingly, the objectives of the present invention are (among others)to circumvent the deficiencies in the prior art and affect the followingobjectives:

-   -   (1) Provide for a touch sensor detector system and method that        does not require individual column drive and row sense circuitry        for each row/column in the sensing array.    -   (2) Provide for a touch sensor detector system and method that        reduces dynamic power consumption when scanning the sense array        by reducing the number of columns that must be driven and the        number of rows sensed to detect pressure/presence at a given        column/row intersection in the sensing array.    -   (3) Provide for a touch sensor detector system and method that        does not require significant electronics integration to support        large area sensing surfaces.    -   (4) Provide for a touch sensor detector system and method that        is capable of sensing contact and pressure with the same device.    -   (5) Provide for a touch sensor detector system and method that        does not require complex manufacturing processes to achieve high        spatial sensing resolutions.    -   (6) Provide for a touch sensor detector system and method that        is compatible with standard PCB manufacturing processes and        methods.    -   (7) Provide for a touch sensor detector system and method that        is amenable to construction in non-planar formats.    -   (8) Provide for a touch sensor detector system and method that        does not require complex calibration procedures to achieve        accurate sensor positioning data.    -   (9) Provide for a touch sensor detector system and method that        produces a linear relationship between sensor data and detected        spatial positioning within the array.    -   (10) Provide for a touch sensor detector system and method that        allows creation of non-rectangular sensors that maintain        accuracy and linearity across the entire sensor.    -   (11) Provide for a touch sensor detector system and method that        allows scanning at varying resolutions while maintaining full        accuracy and linearity.

While these objectives should not be understood to limit the teachingsof the present invention, in general these objectives are achieved inpart or in whole by the disclosed invention that is discussed in thefollowing sections. One skilled in the art will no doubt be able toselect aspects of the present invention as disclosed to affect anycombination of the objectives described above.

BRIEF SUMMARY OF THE INVENTION

The present invention addresses several of the deficiencies in the priorart in the following manner. Rather than utilizing individual columndrivers within a touch sensor array (TSA) to individually drive the TSAcolumns to convey current for individual row sensors to detect, thepresent invention interconnects groups of TSA columns into interlinkedimpedance columns (IICs). These IICs are driven using one of a number ofelectrical column driving sources (CDS) under control of a columnswitching register (CSR). When the TSA internal variable impedance array(VIA) detects a sensor event, individual columns and rows of the VIA areelectrically coupled. This event enables current conduction from theIICs to interlinked impedance rows (IIR) within the VIA. The IIRs arethen selected by a row switching register (RSR) and sensed by ananalog-to-digital converter (ADC).

A computer control device (CCD) permits the TSA to be continuouslyscanned using different configurations of CSR/RSR state as well as CDSdriving parameters. These scans permit the CCD to gather differentialsensor data within the VIA internal to the TSA and interpolate thisinformation to gather a more accurate indication of the sensor profileassociated with the current TSA state. For example, the TSA may beconfigured for scanning at one resolution and then rescanned using adifferent resolution to determine both the focal point of contact withthe TSA but also movement of this focal point over time and across eachTSA scan. Within this context, a focal point of one scanning pass mayalso be used to determine a vector of travel when compared to the focalpoint of subsequent scanning passes. This sensor profile may includeinformation on the exact location of the focal point of sensor activityon the TSA surface as well as other information regarding a moreaccurate indication of sensor detection present at or near the TSAsurface.

In some preferred invention embodiments, the present invention may beapplied to the creation of a low-cost, multi-touch, high resolution,force sensing touch sensor that can be manufactured using traditionalPCB manufacturing methods as well as additive printing techniques. Thepresent invention utilizes the concept of an interpolating array whichallows a high tracking resolution without requiring a large number ofdrive and sense lines to be connected to the sensor scan electronics(active lines). By increasing the tracking resolution relative to thenumber of active drive and sense lines, the present invention allows forincreased sensor performance with reduced electronics complexity andcost as compared to other sensor technologies. Herein are describedseveral possible embodiments for the sensor and how it can be adapted todifferent use cases such as stylus interaction and embedding below orover a display.

In one preferred interpolating force sensing array (IFSA) embodiment,the present invention addresses deficiencies in the prior art by addinga network of resistors to the inputs and outputs of a force sensingarray which decouples the resolution of the force sensing array from theresolution of the drive and sense circuitry. This preferred embodimentelectrically drives and senses the sensor in a fashion that creates abilinear interpolation kernel around each row/column intersection. Thisallows reconstruction of the position of the touch at the resolution ofthe force sensing array, even though the present invention drive andsense circuitry has a much lower resolution. Interestingly, theresolution of the drive and sense circuitry only has an effect on thedistance at which two distinct touches start to look like one to theprocessing algorithms, and does not have an effect on the accuracy withwhich a single touch can be tracked. In addition to the interpolatingresistor network, the present invention teaches several methods ofconstruction for the present invention sensors using known manufacturingtechniques, and it shows the implementation of the driving circuitry,the algorithms for scanning the sensor, and the algorithms forinterpreting the output. It also suggests how the present inventionsensor technology can be integrated with other sensing and displaytechnologies.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the advantages provided by the invention,reference should be made to the following detailed description togetherwith the accompanying drawings wherein:

FIG. 1 illustrates a system block diagram of a preferred exemplarysystem embodiment;

FIG. 2 illustrates a flowchart depicting a preferred exemplary methodembodiment;

FIG. 3 illustrates a system block diagram depicting detail of thevariable impedance array (VIA), interlinked impedance column (IIC), andinterlinked impedance row (IIR);

FIG. 4 illustrates a system block diagram depicting detail of the CSR,RSR, interlinked impedance column (IIC), and interlinked impedance row(IIR);

FIG. 5 illustrates a simplified system block diagram of a preferredexemplary system embodiment;

FIG. 6 illustrates a simplified flowchart depicting a preferredexemplary method embodiment;

FIG. 7 illustrates an exemplary non-orthogonal VIA configuration;

FIG. 8 illustrates exemplary radial and elliptical VIA configurations;

FIG. 9 illustrates an exemplary voltage-mode column drive circuitryschematic;

FIG. 10 illustrates an exemplary voltage-mode column drive circuitryschematic employing a stacked switching design;

FIG. 11 illustrates an exemplary voltage-mode column drive circuitryschematic employing a non-stacked switching design;

FIG. 12 illustrates an exemplary voltage-mode row switching circuitryschematic;

FIG. 13 illustrates an exemplary voltage-mode row switching circuitryschematic incorporating sense line grounding enable logic;

FIG. 14 illustrates an exemplary current-mode column drive circuitryschematic;

FIG. 15 illustrates an exemplary current-mode column drive circuitryschematic employing a stacked switching design;

FIG. 16 illustrates an exemplary current-mode row switching circuitryschematic;

FIG. 17 illustrates an exemplary variable impedance device that may beused for IIC and/or IIR impedance elements;

FIG. 18 illustrates an exemplary active variable impedance array (VIA)element structure;

FIG. 19 illustrates a system block diagram depicting detail of the CSR,RSR, interlinked impedance column (IIC), and interlinked impedance row(IIR) in an embodiment utilizing variable frequency excitation for theVIA and switched filtering detection in the row sense elements;

FIG. 20 illustrates an exemplary VIA depicting a variable frequency scanconfiguration;

FIG. 21 illustrates an exemplary VIA full resolution scan configuration;

FIG. 22 illustrates an exemplary VIA half resolution scan configuration;

FIG. 23 illustrates an exemplary VIA quarter resolution scanconfiguration;

FIG. 24 illustrates an exemplary VIA mixed resolution scanconfiguration;

FIG. 25 illustrates a system block diagram depicting a preferredexemplary invention embodiment employing a pen/stylus input;

FIG. 26 illustrates a perspective diagram depicting a preferredexemplary invention embodiment employing a pen/stylus input;

FIG. 27 illustrates a schematic diagram depicting a preferred exemplarypen/stylus circuit useful in many preferred invention embodiments;

FIG. 28 illustrates a perspective assembly view of a preferred exemplarypen/stylus circuit useful in many preferred invention embodiments;

FIG. 29 illustrates top, bottom, and side views of a preferred exemplarypen/stylus circuit useful in many preferred invention embodiments;

FIG. 30 illustrates a preferred invention embodiment employing apen/stylus and depicts input from hand/finger and pen/stylus inputs;

FIG. 31 illustrates sensed areas of sensed input associated with FIG. 30;

FIG. 32 illustrates sensed areas of sensed input associated with FIG. 30categorized as pressure (P) inputs and stylus (S) inputs;

FIG. 33 illustrates a representative IFSA circuit with four activecolumn electrodes and five active row electrodes incorporating twointerpolating electrodes between each pair of active electrodes;

FIG. 34 illustrates interpolation in a 3 active column by 3 active rowarea of a sensor wherein the sensor has two interpolating electrodesbetween each pair of active electrodes (thus having an N value of 2)wherein is depicted a moment in time during a sensor scan, columns −3and +3 are grounded, and column 0 is driven with a voltage (Vd), whilerows −3 and +3 are grounded and the current flowing from row 0 (Is) ismeasured;

FIG. 35 illustrates a sensitivity distribution for the 7×7 array ofsensor elements shown in FIG. 34 as it is being scanned using thepresent invention drive scheme;

FIG. 36 illustrates a 3D representation of the sensitivity distributionof the 7×7 array of sensors shown in FIG. 34 as it is being scannedusing the present invention drive scheme and depicts linear sensitivityfalloff for sensor elements as they get farther away from theintersection at location (0,0) along both the X and Y axes;

FIG. 37 illustrates an exemplary shunt-mode force sensor with substrateindicated in stripes, drive/sense electrodes indicated with +/−respectively, and FSM indicated in black;

FIG. 38 illustrates an exemplary double-sided thru-mode force sensorwith substrate indicated in stripes, drive/sense electrodes indicatedwith +/− respectively, and FSM indicated in black;

FIG. 39 illustrates an exemplary single-sided thru-mode force sensorwith substrate indicated in stripes, drive/sense electrodes indicatedwith +/− respectively, and FSM indicated in black;

FIG. 40 illustrates an exemplary sandwich thru-mode force sensor withsubstrate indicated in stripes, drive/sense electrodes indicated with+/− respectively, and FSM indicated in black;

FIG. 41 illustrates cross-section and top-down views of a thru-modesensor with segmented FSM (sandwich thru-mode configuration) wherein:with the top-down view, the substrate of the top layer and force sensinglayer (indicated by a pattern of fine dots) are transparent to allow theviewing of the pattern of column electrodes, FSM, and the row electrodesinside; the dashed line indicates the location of the cross-sectionrelative to the sensor; and the patches of force sensing material alignto the intersections of the rows and columns, thus creating a forcesensing element at the intersection of each row and column electrode;

FIG. 42 illustrates cross-section and top-down views of a thru-modesensor with FSM-coated electrodes wherein: with the top-down view, thesubstrate of the top layer is transparent to allow the viewing of thepattern of column electrodes, FSM, and the row electrodes inside; thedashed line indicates the location of the cross-section relative to thesensor; and either the rows, the columns, or both can be coated with FSM(creating a sensor with either a single-sided or double-sided thru-modeconfiguration);

FIG. 43 illustrates cross-section and top-down views of a thru-modesensor with thin FSM electrodes wherein: with the top-down view, thesubstrate of the top layer and the force sensing layer (indicated by apattern of fine dots) are transparent to allow the viewing of the columnelectrodes and the row electrodes inside; the dashed line indicates thelocation of the cross-section relative to the sensor; and the thin FSMcan also be replaced with a patterned FSM or a pseudo-random patternedFSM wherein all of these configurations are variants of the sandwichthru-mode configuration;

FIG. 44 illustrates detail of a thru-mode sensor top layer wherein thediagram is flipped relative to FIG. 41 (4100)-FIG. 43 (4300) to show theelectrode pattern and how the interpolation resistors are mounted;

FIG. 45 illustrates detail of a thru-mode sensor bottom layer. The layerin this diagram is in the same orientation as in FIG. 41 (4100)-FIG. 43(4300);

FIG. 46 illustrates detail of a segmented FSM layer wherein the segmentsof FSM material are shown in black and the substrate holding the FSMmaterial in place is white with a pattern of fine dots and each segmentaligns with a single sensor element (at the intersection of a row andcolumn electrode), ensuring that there is no cross-talk between sensorelements. This is the same FSM layer as shown in FIG. 41 (4100) thatdepicts the FSM layer being used in a thru-mode sensor configuration.This type of FSM configuration can also be used as the force sensinglayer in any shunt-mode sensor configuration;

FIG. 47 illustrates detail of a thin FSM layer wherein the FSM materialis shown in black, is contiguous, and covers the entire sensor areacontaining row and column electrodes. Because the material is thin, thein-plane resistance is very high which reduces the possibility ofcross-talk between sensor elements. This is the same FSM layer as shownin FIG. 43 (4300) which shows the FSM layer being used in a thruconfiguration can also be used as the force sensing layer in anyshunt-mode sensor configuration;

FIG. 48 illustrates detail of a patterned FSM layer wherein the patchesof FSM material are shown in black and the substrate holding the FSMmaterial in place is shown in white. Because the pattern is finer thanthe scale of individual sensor elements, cross-talk between neighboringsensor elements is minimized. This can be used instead of the thin FSMlayer shown in FIG. 47 (4700) in a thru-mode sensor configuration. Thistype of FSM configuration can also be used as the force sensing layer inany shunt-mode sensor configuration;

FIG. 49 illustrates detail of a pseudo-random patterned FSM layerwherein the patches of FSM material are shown in black and the substrateholding the FSM material in place is shown in white. This is similar tothe patterned FSM, but a random or pseudo-random pattern is used, whichmay be easier to manufacture than the patterned FSM layer. This can beused instead of the thin FSM layer shown in FIG. 48 (4800) in athru-mode sensor configuration. This type of FSM configuration can alsobe used as the force sensing layer in any shunt-mode sensorconfiguration;

FIG. 50 illustrates a cross-section and top-down view of a shunt-modeinterpolating array sensor which consists of a top patterned FSM and abottom layer which carries interpolating resistors and both row andcolumn electrodes. In the top-down view, the patterned FSM layer is cutaway to reveal the exposed row and column electrodes which lie below theFSM, forming shunt-mode sensor elements. The dashed line indicates thelocation of the cross-section relative to the sensor. Traces on thereverse side of the bottom layer (not visible in the top-down view)interconnect the exposed row electrodes using vias (represented bycircles). The traces on the reverse side of the bottom layer are shownin more detail in FIG. 52 (5200);

FIG. 51 illustrates a cross-section and top-down view of a shunt-modesensor with force sensor element electrodes patterned in aninter-digitated finger pattern, which is intended to improvesensitivity. Other elements in this design are similar to thosedescribed in FIG. 50 (5000);

FIG. 52 illustrates a detail of the reverse side of the bottom layer forsensors shown in FIG. 50 (5000)-FIG. 51 (5100). The areas with a stripedpattern are conductors which interconnect the row electrodes. Vias,which are represented by circles, connect to the row electrodes on theopposite side;

FIG. 53 illustrates a cross-section and top-down view of a shunt-modesensor with double-width row electrode pad, which halves the number ofvias necessary by sharing vias between adjacent sensor elements, andalso increases the space around each via which may aid manufacturing.Other elements in this design are similar to those described in FIG. 50(5000). The traces on the reverse side of the bottom layer are shown inmore detail in FIG. 55 (5500);

FIG. 54 illustrates a cross-section and top-down view of a shunt-modesensor with double-width row electrode pads and inter-digitated fingerrow electrode pattern. This design has the same manufacturing advantageas the previous design and the inter-digitating finger pattern, similarto that shown in FIG. 51 (5100), and is intended to improve sensitivity.Other elements in this design are similar to those described in FIG. 51(5100). The traces on the reverse side of the bottom layer are shown inmore detail in FIG. 55 (5500);

FIG. 55 illustrates a detail of the reverse side of the bottom layer forsensors shown in FIG. 53 (5300)-FIG. 54 (5400). The areas with a stripedpattern are conductors which interconnect the row electrodes. Vias,which are represented by circles, connect to the row electrodes on theopposite side;

FIG. 56 illustrates a cross-section and top-down view of shunt-modesensor with diamond-shaped row and column electrode pattern. Thispattern is intended to make the sensitivity distribution around eachrow/column intersection more symmetric. It may also improvemanufacturability by reducing the precision needed when creating vias.Other elements in this design are similar to those described in FIG. 50(5000). The traces on the reverse side of the bottom layer are shown inmore detail in FIG. 57 (5700);

FIG. 57 illustrates a detail of the reverse side of the bottom layer forsensor shown in FIG. 56 (5600). The areas with a striped pattern areconductors which interconnect the row electrodes. Vias, which arerepresented by circles, connect to the row electrodes on the oppositeside;

FIG. 58 illustrates a cross-section and top-down view of a shunt-modeoval sensor with a hole in the center. The FSM layer is removed toexpose the row and column electrode pattern. Circles represent vias thatinterconnect with the bottom conductor pattern shown in FIG. 60 (6000);

FIG. 59 illustrates a design of a FSM layer for an oval sensor shown inFIG. 58 (5800). This design shows a segmented FSM sensor pattern, butother types of FSM patterns including the ones shown in FIG. 47(4700)-FIG. 49 (4900) can be used;

FIG. 60 illustrates detail of a reverse side of the bottom layer for theoval sensor shown in FIG. 58 (5800). The areas with a striped patternare conductors which interconnect the row electrodes. Vias, which arerepresented by circles, connect to the row electrodes on the oppositeside;

FIG. 61 illustrates diamond pattern shunt-mode IFSA with bridges. Thispattern is created by creating pattern of rows and columns (the columnsare contiguous but the row pattern has breaks) (6101); depositinginsulating material in areas where columns travel between rows (6102);and depositing patches of conductive material that bridges the padsbelonging to each row without electrically connecting to the columns(6103);

FIG. 62 illustrates how an IFSA sensor designed with cuts and bend linescan be bent into complex shapes. In this example, the pattern on theleft can be bent to form a sensor for a robot fingertip as shown on theright;

FIG. 63 illustrates four cross-sections of possible IFSA Sensorstackups;

FIG. 64 illustrates four cross-sections of possible IFSA Sensor stackupswhich include a display;

FIG. 65 illustrates a top right front perspective view of a preferredexemplary invention embodiment as applied to a tablet form factorinterface application context;

FIG. 66 illustrates a top right rear perspective assembly view of apreferred exemplary invention embodiment as applied to a tabletinterface application context;

FIG. 67 illustrates a top right front perspective view of a basecomponent of a preferred exemplary invention embodiment as applied to atablet interface application context;

FIG. 68 illustrates a top right front perspective view of a PCB/batterycomponent of a preferred exemplary invention embodiment as applied to atablet interface application context;

FIG. 69 illustrates a top view of a PCB/battery component of a preferredexemplary invention embodiment as applied to a tablet interfaceapplication context;

FIG. 70 illustrates a top right front perspective view of a pressuremembrane component of a preferred exemplary invention embodiment asapplied to a tablet interface application context;

FIG. 71 illustrates a top right front perspective view of an overlaycomponent of a preferred exemplary invention embodiment as applied to atablet interface application context;

FIG. 72 illustrates a top right front perspective view of a bezelcomponent of a preferred exemplary invention embodiment as applied to atablet interface application context;

FIG. 73 illustrates a front cross section view of a preferred exemplaryinvention embodiment as applied to a tablet interface applicationcontext;

FIG. 74 illustrates a detail perspective view of a USB connector in apreferred exemplary invention embodiment as applied to a tabletinterface application context;

FIG. 75 illustrates a detail perspective side cross section view in apreferred exemplary invention embodiment as applied to a tabletinterface application context;

FIG. 76 illustrates a side cross section view of a preferred exemplaryinvention embodiment as applied to a tablet interface applicationcontext;

FIG. 77 illustrates an exemplary system block diagram schematic for apressure sensitive touch pad embodiment of the present invention;

FIG. 78 illustrates an exemplary top copper layout for a pressuresensitive touch pad embodiment of the present invention;

FIG. 79 illustrates an exemplary bottom copper layout for a pressuresensitive touch pad embodiment of the present invention;

FIG. 80 illustrates an exemplary via layout for a pressure sensitivetouch pad embodiment of the present invention;

FIG. 81 illustrates a top view of an exemplary embodiment of a presentinvention capacitive sensor layout employing a single-sided diamondpattern with bridges;

FIG. 82 illustrates a sectional view of an exemplary embodiment of apresent invention capacitive sensor layout employing a single-sideddiamond pattern with bridges;

FIG. 83 illustrates a top view of an exemplary embodiment of a presentinvention capacitive sensor layout employing a double-sided pattern withstraight rows and columns;

FIG. 84 illustrates a sectional view of an exemplary embodiment of apresent invention capacitive sensor layout employing a double-sidedpattern with straight rows and columns;

FIG. 85 illustrates an exemplary touch sensor tablet contacting adrinking cup to produce a pressure profile;

FIG. 86 illustrates the TSM data obtained by the CCD by scanning theTSA, and the associated pressure regions detected;

FIG. 87 illustrates an approximate reconstruction of the forces seen byindividual force sensing elements in the VIA obtained by performing anupsampling operation of the TSM and the associated pressure regionsdetected;

FIG. 88 illustrates exemplary individual detected ellipse data computedby the CCD based on the TSM data;

FIG. 89 illustrates an exemplary touch sensor tablet contacting apaintbrush to produce a pressure profile;

FIG. 90 illustrates the pressure profile of the TSM data obtained by theCCD by scanning the TSA;

FIG. 91 illustrates the associated pressure regions detected based onthe pressure profile;

FIG. 92 illustrates exemplary individual detected ellipse data computedby the CCD based on the TSM data;

FIG. 93 illustrates an interpolating capacitive touch sensor system thattransmits a single frequency from a single active drive electrode to asingle active receive electrode;

FIG. 94 illustrates an interpolating capacitive touch sensor system thattransmits a single frequency from a single active drive electrode tomultiple active receive electrodes;

FIG. 95 illustrates an interpolating capacitive touch sensor system thattransmits multiple frequencies from multiple active drive electrodes tomultiple active receive electrodes;

FIG. 96 illustrates an interpolating capacitive touch sensor system thattransmits a single frequency from a single active drive electrode to areceiving stylus;

FIG. 97 illustrates an interpolating capacitive touch sensor system thatreceives a single frequency from a transmitting stylus on a singleactive receive electrode;

FIG. 98 illustrates an interpolating capacitive touch sensor system thattransmits and receives a single frequency from a bi-directional stylusto a single active bidirectional electrode;

FIG. 99 illustrates a sensor that combines an interpolating capacitivetouch sensor system with an interpolating resistive touch sensor system;

FIG. 100 illustrates circuitry that generates a square wave transmissionsignal using a PWM module and an analog switch;

FIG. 101 illustrates circuitry that generates a square wave transmissionsignal using a PWM module and a comparator;

FIG. 102 illustrates circuitry that generates a sine wave transmissionsignal using a phase-shift oscillator, a voltage follower, and an analogswitch;

FIG. 103 illustrates circuitry that generates a sine wave transmissionsignal using a sine wave lookup table, a DAC, a filter, and anamplifier;

FIG. 104 illustrates circuitry that converts a received AC signal into aDC signal that can be read by an ADC, where the DC value corresponds tothe receive strength of the AC signal;

FIG. 105 illustrates circuitry that captures an AC waveform comprisingof multiple frequencies;

FIG. 106 illustrates using an FFT on a captured waveform to determinethe frequency composition of a signal;

FIG. 107 illustrates a stackup that adds force sensitivity to aninterpolating capacitive touch sensor through the use of a conductivefilm adhered to the underside of a flexible top layer and a deformablemiddle layer;

FIG. 108 illustrates a stackup that adds an interpolating capacitivetouch sensor on top of a display, with an optional EMR sensorunderneath;

FIG. 109 illustrates the non-linear tracking of a standard capacitivetouch sensor configuration with a 4 millimeter electrode and patternpitch;

FIG. 110 illustrates a cross section (with visible electric-field lines)of a standard capacitive touch sensor configuration with a 4 millimeterelectrode and pattern pitch;

FIG. 111 illustrates the improved sensor linearity of an interpolatingcapacitive touch sensor configuration with a 4 millimeter activeelectrode pitch and a 1 millimeter pattern pitch;

FIG. 112 illustrates a cross section (with visible electric-field lines)of an interpolating capacitive touch sensor configuration 4 millimeteractive electrode pitch and a 1 millimeter pattern pitch;

FIG. 113 illustrates the response of a standard existing capacitivetouch sensor solution;

FIG. 114 illustrates the response of an interpolating capacitive touchsensor solution;

FIG. 115 illustrates the upsampled output of an interpolating capacitivetouch sensor solution;

FIG. 116 illustrates a flowchart depicting the scanning method for aninterpolating capacitive touch sensor;

FIG. 117 illustrates a flowchart depicting the scanning methodsubroutines for an interpolating capacitive touch sensor system thatembodies the structure shown in FIG. 93 ;

FIG. 118 illustrates a flowchart depicting the scanning methodsubroutines for an interpolating capacitive touch sensor system thatembodies the structure shown in FIG. 95 ;

FIG. 119 illustrates a flowchart depicting the scanning method for aninterpolating capacitive touch sensor with an active stylus;

FIG. 120 illustrates a flowchart depicting the scanning methodsubroutines for an interpolating capacitive touch sensor with an activestylus that embodies the structure of FIG. 96 ;

FIG. 121 illustrates a flowchart depicting the scanning methodsubroutines for an interpolating capacitive touch sensor with an activestylus that embodies the structure of FIG. 97 ;

FIG. 122 illustrates a flowchart depicting the scanning method for asensor that embodies the structure of FIG. 99 ;

FIG. 123 illustrates a flowchart depicting an alternate method forscanning a sensor that embodies the structure of FIG. 99 ;

FIG. 124 illustrates the measured signal of an active capacitive stylusinteracting with an interpolating capacitive sensor at each active rowand column electrode; and

FIG. 125 illustrates a matrix of possible detection states for a givencontact when using a sensor capable of both capacitive andforce-sensitive touch sensing.

DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS

While the present invention is susceptible of embodiment in manydifferent forms, there is shown in the drawings and will herein bedescribed in detailed preferred embodiments of the invention with theunderstanding that the present disclosure is to be considered as anexemplification of the principles of the invention and is not intendedto limit the broad aspect of the invention to the embodimentillustrated.

The numerous innovative teachings of the present application will bedescribed with particular reference to the presently preferredembodiment, wherein these innovative teachings are advantageouslyapplied to the particular problems of a TOUCH SENSOR SYSTEM AND METHOD.However, it should be understood that this embodiment is only oneexample of the many advantageous uses of the innovative teachingsherein. In general, statements made in the specification of the presentapplication do not necessarily limit any of the various claimedinventions. Moreover, some statements may apply to some inventivefeatures but not to others.

IIC/IIR Order Not Limitive

The present invention may utilize a variety of different configurationsof interlinked impedance columns (IIC) and interlinked impedance rows(IIR). In many preferred embodiments there will be two or more IICs andtwo or more IIRs, thus permitting a reduction of both the number of VIAexternally accessible columns and rows by a factor of two or more in thecolumn and row orientations. However, some preferred inventionembodiments may utilize a singular inter-column impedance element or asingular inter-row impedance element in one or more columns/rows. Thus,the terms IIC and IIR encompass the condition in which only onedimension of the VIA incorporates an interlinked impedance element.

Column Driving Source (CDS) Not Limitive

The present invention may utilize a wide variety of sources to drive theVIA sensor columns, including but not limited to: DC voltage source; ACvoltage source; arbitrary waveform generator (AWG) voltage source; DCcurrent source; AC current source; and arbitrary waveform generator(AWG) current source. Note that the use of AWG sources in this contextmay include a wide variety of signaling waveforms that may bedynamically defined/generated using conventional waveform generationtechniques well known in the electrical arts.

CSR/RSR Sources/Sinks Not Limitive

The present invention may utilize a wide variety of electrical sourcesand electrical sinks within the column switching register (CSR) and rowswitching register (RSR) to configure stimulation and/or sensing of theVIA. Within this context, the present invention anticipates the use ofCSR sources selected from a group consisting of: open circuit; zeropotential voltage source; voltage source defined by the CSR; currentsource defined by the CSR; voltage derived from the CDS; and currentderived from the CDS. Within this context the present inventionanticipates the use of RSR sinks selected from a group consisting of:open circuit; zero potential voltage source; voltage source defined bythe RSR; current sink defined by the RSR; and the input to an ADC.

IIC/IIR Resistors Not Limitive

The resistors depicted in the exemplary IIC and IIR functionalitydescribed herein may be fixed resistors (possibly of varying values)and/or may include variable resistors that in some circumstances may beconfigured based on the CSR and/or RSR. Within this context, theresistors depicted are to be considered as one potential example of ageneral impedance, which may include any combination of resistance,capacitance, and/or inductance. Other types of impedance elements suchas capacitive or inductive elements, active elements (or activecircuitry) as well as combinations of these may be substituted for thedepicted resistors with no loss of generality in the scope of theclaimed invention. Thus, in the context of the IIC and IIR circuitry,any form of impedance may be substituted for the illustrated resistorelements, and may include variable impedance elements including activecomponents such as MOSFETs and other semiconductor devices.

Inter-Column/Inter-Row Impedance Count Not Limitive

The present invention uses inter-column impedances and inter-rowimpedances in conjunction with inter-column and inter-row interpolationwithin the VIA to implement the touch sensor detector system and method.The number of impedances between each column and each row is typicallyconfigured as two or more, but in some circumstances the VIA may bedirectly mapped to achieve conventional scanning of all VIA columns/rowsvia access to internal nodes within the series IIC and IIR impedancestrings.

Row/Column Not Limitive

The present invention will be discussed in terms of rows/columns whenaddressing a typical configuration in which the touch sensor array (TSA)is configured as a conventional array of variable impedance sensors(VIA). However, the terms “row” and “column” may be interchanged in manyinvention embodiments without departing from the overall spirit andscope of the claimed invention.

Sensor Array Geometry not Limitive

The present invention anticipates a wide variety of sensor arraygeometries that may be used depending on the application context. Whilerectangular construction arrays of variable impedance elements may beadvantageous in some preferred invention embodiments, the use of othergeometries including polygons, circles, ellipses, and other planar andnon-planar shapes are also anticipated. The application of the disclosedtechnology to both two-dimensional and three-dimensional shapes isanticipated within this broad scope of sensor geometry.

Sensor VIA Population Not Limitive

The present invention anticipates that in some applications the VIAsensor array may be partially populated such that a sensor element mayonly be present in a subset of the overall VIA structure. For example, asensor configuration in which the VIA further comprises physical columnselectrically coupled to physical rows via a pressure-sensitive sensorelement located at the intersections of the physical columns and thephysical rows is anticipates wherein the pressure-sensitive sensorelement is present in only a subset of the intersections to form ashaped sensor array. This permits a reduction in overall VIA sensormanufacture and creates the possibility of custom sensor applicationsand shapes/physical configurations which in some circumstances may havevarying degrees of sensor density across the VIA array.

ADC Not Limitive

The present invention illustrates in many preferred embodiments the useof an analog-to-digital converter (ADC). This ADC may be implemented insome embodiments as a voltage mode converter and in other embodiments asa current mode converter. Furthermore, some preferred ADC embodimentsmay incorporate frequency detection/filtering so as to enable frequencydiscrimination within the analog-to-digital conversion process.

Sensor Element Not Limitive

The present invention may be applied to a wide variety of variableimpedance array (VIA) touch sensor technologies such as pressuresensors, capacitance sensors, optical sensors, photo-sensitive sensors,and RF-based sensor technologies. These technologies may in somecircumstances be combined to form hybrid sensor systems. In somecircumstances, the sensor array may detect near-field events that do notnecessarily touch the sensing surface of the VIA sensors. Within thiscontext, the individual sensing elements may also be referred to as“sensor elements” within this document.

Post-Processing Not Limitive

The present invention in many preferred embodiments generates a TouchSensor Matrix (TSM) representing information collected from the VIA.This TSM data structure may be transmitted by the computing controldevice (CCD) to a digital data processor (DDP), or locally processed bythe CCD to perform a variety of application-specific functions.

TSM Collection/Processing Not Limitive

The Touch Sensor Matrix (TSM) representing information collected fromthe VIA may be collected and/or processed as an entire entity or may insome circumstances be collected and/or processed in a piece-mealfashion. This may occur (for example) in situations where an area of thetouch sensor detector is scanned and VIA information collected andprocessed from this partial region of interest. Similarly, this partialinformation may be transmitted by the computing control device (CCD) toa digital data processor (DDP), or locally processed by the CCD toperform a variety of application-specific functions associated with thepartially scanned area of the detector. Thus, any transfer or processingof the TSM assumes that a partial transfer or processing of the matrixis also anticipated.

Conceptual Overview

The present invention relates to the field of multi-touch touch sensors,which are commonly used to add touch input to computers, tablets, andother electronic devices. Multi-touch sensing refers to the ability of atouch sensor to distinguish and independently track multiple touches,which allows users to interact with the sensor using multiple hands,fingers, or other objects (such as styli) simultaneously, and alsoallows for multiple users to interact with the sensor simultaneously.While many touch sensing technologies only allow for the determinationof the presence/absence of a touch and its position, the presentinvention technologies also have the ability to determine the amount offorce that is being exerted at each touch point.

The present invention also relates to the field of pressure-sensitivearrays which are often used in industrial and medical applications tomeasure pressure distributions over an area and to detect variations inpressure, including contact areas, peaks, and minima in a pressuredistribution.

Operational Goals

Within the context of a conventional touch sensor array, a variableimpedance array (VIA) senses touches at a particular resolution (at theresolution of the sensor elements). This is the highest resolution ofdata possible if every row and column of the VIA were to be individuallyconnected to driving/sensing electronics. Within the context of thepresent invention, interpolation blocks (interlinked impedance columns(IIC) and interlinked impedance rows (IIR)) allow the VIA sensors to bescanned at a lower resolution. Because of the configuration of the IICand IIR, the sensor hardware can properly downsample the signal in theVIA (in a linear fashion). As a result, the scanned values in thelower-resolution array (touch sensor matrix (TSM) data structure)extracted from this VIA sensor data resemble that of a linearlydownsampled sensor response. This downsampling allows reconstruction ofthe positions, force, shape, and other characteristics of touches at theresolution of the VIA (and even possibly at a higher resolution than theVIA) in software.

As an example, on a VIA sensor array constructed with 177 columnelectrodes and 97 row electrodes having a 1.25 mm pitch, it could bepossible in theory to build electronics with 177 column drive lines and97 row sense lines to support sensing of this entire VIA. However, thiswould be prohibitive in terms of cost and it would be very difficult toroute that many row and sense lines on a conventional printed circuitboard (PCB) in a space efficient manner. Additionally, this 177×97 VIAsensor configuration would require scanning 177×97=17169 intersections,which with a low power microcontroller (such as an ARM M3) would resultin a maximum scan rate of approximately 10 hz (which is unacceptablyslow for typical user interaction with a touch screen). Finally,assuming 16-bit ADC values, storage for these touch screen values wouldrequire 17169×2=34 KB of memory for a single frame, an excessive memoryrequirement for small microcontrollers that may only be configured with32 KB of RAM. Thus, the use of conventional row/column touch sensortechnology in this context requires a much more powerful processor andmuch more RAM, which would make this solution too expensive and complexto be practical for a consumer electronics application.

The gist of the invention is that rather than scanning the exemplarysensor array described above at the full 177×97 resolution, the systemis configured to scan at a lower resolution, but retain the accuracy andquality of the signal as if it had been scanned at 177×97. To continuediscussion of the example sensor array above, the drive electronics on atypical present invention embodiment for this sensor array would requireonly 45 column drivers and 25 row drivers. The interpolation circuitallows the system to scan the 177×97 array using only a complement of45×25 electronics. This cuts the number of intersections that must bescanned down by a factor of 16 to 45×25=1125. This configuration allowsscanning the sensor at 150 Hz and reduces memory consumption in aRAM-constrained microcontroller application context. Although theability to resolve two touches that are 1.25 mm together (or to seeexactly what is happening at each individual sensor element) is lost, itis still possible to track a touch at the full resolution of the VIAsensors because of the linearity of the row/column interpolationperformed by using the IIC and IIR.

System Overview (0100)

A general view of a preferred exemplary system embodiment in a typicalapplication context is depicted in FIG. 1 (0100), wherein a user (0101)interacts with a graphical user interface (GUI) (0102) that incorporatesa computer (typically consisting of a mobile or non-mobile computingdevice and herein collectively described as a digital data processor(DDP)) (0103) executing machine instructions read from a computeruseable medium (0104). In this application context, the preferredexemplary touch sensor detector (0110) system embodiment incorporates atouch sensor array (0111) that comprises a variable impedance array(VIA) (0112).

The VIA (0112) may utilize a resistive or capacitive array consisting ofrows and columns of sensor elements that may be arranged in aconventional orthogonal orientation, or in some circumstances, the VIA(0112) may be configured wherein the row/columns are not orthogonal toeach other (as depicted in the example illustrated in FIG. 7 (0700)).The VIA (0112) has interlinked impedance columns (IIC) (0113) andinterlinked impedance rows (IIR) (0114) at its edges that may beconfigured to electrically connect, stimulate, or sense two or morecolumns/rows (via internal electrical column/row nodes within the (IIC)(0113) and (IIR) (0114)) in various configurations of connectivity.

The IIC (0113) and IIR (0114) are controlled by an array column driver(ACD) (0115) and array row sensor (ARS) (0116). The ACD (0115) isresponsible for selecting the configuration of the IIC (0113), theelectrical sources that are used to drive the IIC (0113), and theselection of columns that are electrically driven within the IIC (0113).The ARS (0116) is responsible for selecting the configuration of the IIR(0114), the electrical sinks that are connected to the IIR (0114), andthe selection of rows that are electrically sensed within the IIR(0114). The ACD (0115) and ARS (0116) are controlled with drive/sensecontrol circuitry (0117) that may include individual column switchingregisters (CSR) and row switching registers (RSR), as well asdigital-to-analog converters (DAC) used to drive the IIC (0113) via theACD (0115) and/or analog-to-digital (ADC) converters used to sense theconfigured IIR (0114) status through the ARS (0116).

The sensed results of reading analog signals from the ARS (0116) may beconverted to digital by the drive/sense control circuitry (0117) andpresented to a digital interface (0118) for transmission to thecomputing system (0103) and interpretation by operating system softwarein the context of application software running on the computer (0103). Awide variety of computer systems (0103) and associated applications areanticipated in this system context.

The system as depicted differs from the prior art in that configurationof the IIC (0113) and IIR (0114) as determined by the ACD (0115) and ARS(0116), permits the VIA (0112) sensing elements to be interfaced withless complex electronics (fewer column drivers and fewer row sensors)while still providing spatial granularity that is comparable to thephysical row/column spacing present in the VIA (0112). By manipulationof the IIC (0113) and IIR (0114) configuration and the use ofappropriate software in the drive/sense control circuitry (0117), VIA(0112) sensing elements may be interpolated through a coarser hardwareinterface that does not require active circuitry to support eachindividual row and column within the VIA (0112). This interpolationcapability is a combination of various hardware configurations of theIIC (0113) and IIR (0114) in combination with a variety of softwaretechniques within the drive/sense control circuitry (0117) that may beused to refine the raw data collected by the ARS (0116).

Within this context, a variety of methods of electrically driving theVIA (0112) columns and sensing the VIA (0112) rows is anticipatedincluding both DC and AC signaling as well as the use of both voltagemode and current mode drive/sensing methodologies.

Method Overview (0200)

An exemplary present invention method can be generally described in theflowchart of FIG. 2 (0200) as incorporating the following steps:

-   -   (1) Configure interlinked impedance columns (IIC) within        variable impedance array (VIA) (0201);    -   (2) Configure interlinked impedance rows (IIR) within VIA        (0202);    -   (3) Electrically stimulate IIC with column driving electrical        source (CDS) (0203);    -   (4) Sense electrical response in IIR with ADC and convert to        digital format (0204);    -   (5) Store IIR converted digital format response in a touch        sensor matrix (TSM) data structure (0205);    -   (6) Determine if predetermined CDR/IIC/IIR variations have been        logged to the TSM, and if so, proceed to step (8) (0206);    -   (7) Reconfigure CDS/IIC/IIR for the next VIA sensing variant and        proceed to step (3) (0207);    -   (8) Interpolate TSM values to determine focal points of activity        within the VIA (0208);    -   (9) Convert focal point activity information into user interface        input command sequence (0209); and    -   (10) Transmit user interface input command sequence to a        computer system for action and proceed to step (1) (0210).

This general method may be modified heavily depending on a number offactors, with rearrangement and/or addition/deletion of stepsanticipated by the scope of the present invention. Integration of thisand other preferred exemplary embodiment methods in conjunction with avariety of preferred exemplary embodiment systems described herein isanticipated by the overall scope of the present invention.

VIA/IIC/IIR Detail (0300)

Additional detail of the variable impedance array (VIA) (0310),interlinked impedance columns (IIC) (0320), and interlinked impedancerows (IIR) (0330) is generally depicted in FIG. 3 (0300). Here the VIA(0310) includes columns (0312) and rows (0313) of an array in whichindividual variable impedance array elements (0319) may interconnectwithin the row/column crosspoints of the array. These individualvariable impedance array elements (0319) may comprise active and/orpassive components based on the application context, and include anycombination of resistive, capacitive, and inductive components. Thus theVIA (0310) array impedance elements (0319) are depicted generically inthis diagram as generalized impedance values Z.

It should be noted that the physical VIA columns (0312) and VIA rows(0313) are connected together via interlinked impedance columns (IIC)(0320) and interlinked impedance rows (IIR) (0330), respectively. TheIIC (0320) and IIR (0330) are configured to reduce the number of columnsand rows that are connected to the column drive sources (0321, 0323,0325) and the row sense sinks (0331, 0333, 0335). As such, thecombination of the IIC (0320) and IIR (0330) will reduce the externalcomponents necessary to interface to the VIA columns (0312) and VIA rows(0313). Within the context of the present invention, the number of IIC(0320) interconnects will be configured to allow the reduction of thenumber of column drive sources (0321, 0323, 0325) to less than thenumber of physical VIA columns (0312) (thus the number of external IICcolumns is typically less than the number of internal IIC columns), andthe IIR (0330) interconnects will be configured to allow the reductionof the number of row sense sinks (0331, 0333, 0335) to less than thenumber of physical VIA rows (0313) (thus the number of external IIR rowsis typically less than the number of IIR rows). This reduction isachieved by having one or more IIC (0320) elements (0329) in seriesbetween each VIA physical column (0312) and one or more IIR (0330)elements (0339) between each VIA physical row (0313). Thus, the XXY VIAsensor (0310) is translated to an electrical interface only requiring Pcolumn drivers and Q row sensors. The present invention constrainsP≤X  (1)and

≤Y  (2)with many preferred embodiments satisfying the relations

$\begin{matrix}{\frac{X}{P} \geq 2} & (3)\end{matrix}$ or $\begin{matrix}{\frac{Y}{Q} \geq 2} & (4)\end{matrix}$Note that within the context of these preferred embodiments, there maybe circumstances where the IIC may incorporate a plurality ofinterlinked impedances with the IIR incorporating a singular interlinkedimpedance element, and circumstances where the IIC may incorporate asingular interlinked impedance element with the IIR incorporating aplurality of interlinked impedance elements.

The IIC (0320) impedance elements (0329) are configured to connectindividual VIA columns (0312). These IIC (0320) impedance elements(0329) may comprise active and/or passive components based on theapplication context and include any combination of resistive,capacitive, and inductive components. Thus the IIC (0320) impedanceelements (0329) are depicted generically in this diagram as generalizedimpedance values X. As depicted in the diagram, the individual VIAcolumns may either be directly driven using individual column drivesources (0321, 0323, 0325) or interpolated (0322, 0324) between thesedirectly driven columns.

The IIR (0330) impedance elements (0339) are configured to connectindividual VIA rows (0313). These IIR (0330) impedance elements (0339)may comprise active and/or passive components based on the applicationcontext and include any combination of resistive, capacitive, andinductive components. Thus the IIR (0330) impedance elements (0339) aredepicted generically in this diagram as generalized impedance values Y.As depicted in the diagram, the individual VIA rows may either bedirectly sensed using individual row sense sinks (0331, 0333, 0335) orinterpolated (0332, 0334) between these directly sensed rows.

The column drive sources (0321, 0323, 0325) are generically illustratedas being independent in this diagram, but may be combined in someconfigurations utilizing a series of switches controlled by a columnswitching register (CSR) that defines the type of column drive source tobe electrically coupled to each column that is externally accessible tothe VIA sensors (0310). Variations of AC/DC excitation, voltage sources,open circuits, current sources, and other electrical source drivercombinations may be utilized as switched configurations for the columndrive sources (0321, 0323, 0325). The CSR may be configured to bothselect the type of electrical source to be applied to the VIA sensors(0310) but also its relative amplitude/magnitude.

The row sense sinks (0331, 0333, 0335) are generically illustrated asbeing independent in this diagram but may be combined in someconfigurations utilizing a series of switches controlled by a rowswitching register (RSR) that defines the type of row sense sinks to beelectrically coupled to each row that is externally accessible to theVIA sensors (0310). Variations of AC/DC excitation, voltage sources,open circuits, current sources, and other electrical sense sinkcombinations may be utilized as switched configurations for the rowsense sinks (0331, 0333, 0335). The RSR may be configured to both selectthe type of electrical sink to be applied to the VIA sensors (0310), butalso its relative amplitude/magnitude.

Column/Row Switching Logic (0400)

Further detail of the CSR and RSR column/row source/sink operation isdepicted in FIG. 4 (0400) wherein the VIA (0410) is interfaced via theuse of the IIC (0412) and IIR (0413) impedance networks to column drivesources (0421, 0423, 0425) and row sense sinks (0431, 0433, 0435),respectively. The column switching registers (CSR) (0420) may comprise aset of latches or other memory elements to configure switchescontrolling the type of source drive associated with each column drivesource (0421, 0423, 0425), the amplitude/magnitude of the drive source,and whether the drive source is activated. Similarly, the row switchingregisters (RSR) (0430) may comprise a set of latches or other memoryelements to configure switches controlling the type of sense sinkassociated with each row sense sink (0431, 0433, 0435), theamplitude/magnitude of the sink, and whether the sink is activated.

As mentioned previously, the IIC (0412) and IIR (0413) impedancenetworks may comprise a wide variety of impedances that may be static oractively engaged by virtue of the configuration of the CSR (0420) andRSR (0430), respectively. Thus, the CSR (0420) and RSR (0430) may beconfigured in some preferred embodiments to not only stimulate/sense theVIA (0410) behavior, but also internally configure the interlinkednature of the VIA (0410) by reconfiguring the internal columncross-links and the internal row cross-links. All of this behavior canbe determined dynamically by virtue of control logic (0440) that mayinclude a microcontroller or other computing device executing machineinstructions read from a computer-readable medium (0444). Within thiscontext, the behavior of the analog-to-digital (ADC) converter (0450)may be controlled in part by the configuration of the CSR (0420) and/orRSR (0430), as well as the control logic (0440). For example, based onthe configuration of the CSR (0420) and RSR (0430), the ADC (0450) maybe configured for specific modes of operation that are compatible withthe type of sensing associated with the CSR (0420)/RSR (0430) setup.

Simplified System Embodiment (0500)

The generalized concepts depicted in FIG. 1 (0100)-FIG. 4 (0400) may besimplified in some system designs as depicted in FIG. 5 (0500). Here aVIA sensor (0510) is depicted in which the interlinked impedance columns(0520) form a reduced electrical interface to the physical VIA sensorcolumns (0512) that comprise the VIA sensor array (0510). Similarly, theinterlinked impedance rows (0530) form a reduced electrical interface tothe physical VIA sensor rows (0513) that comprise the VIA sensor array(0510). Note in this example that the number of physical VIA columns(0512) need not be the same as the number of physical VIA rows (0513).Furthermore, the number of column interpolation impedance components (X)serially connecting each column of the VIA (0510) need not be equal tothe number of row interpolation impedance components (Y) seriallyconnecting each row of the VIA (0510). In other words, the number ofinterpolated columns (0522, 0524) need not be equal to the number ofinterpolated rows (0532, 0534).

The control logic (0540) provides information to control the state ofthe column switches (0521, 0523, 0525) and row switches (0531, 0533,0535). The column switches (0521, 0523, 0525) define whether theindividual VIA columns are grounded or driven to a voltage potentialfrom a voltage source (0527) that may in some embodiments be adjustableby the control logic (0540) to allow on-the-fly adjustment (0541) whichcan be used to compensate for potential non-linearities in the drivingelectronics. Similarly, the row switches (0531, 0533, 0535) definewhether an individual VIA row is grounded or electrically coupled to thesignal conditioner (0560) and associated ADC (0550).

In the configuration depicted in FIG. 5 (0500), the VIA sensors (0510)comprise uniformly two interpolating impedances between each column (X)and three interpolating impedances between each row (Y). Thisillustrates the fact that the number of interpolating columns need notequal the number of interpolating rows in a given VIA. Furthermore, itshould be noted that the number of interpolating columns need not beuniform across the VIA, nor does the number of interpolating rows needbe uniform across the VIA. Each of these parameters may vary in numberacross the VIA.

Note also that the VIA sensors (0510) need not have uniformity withinthe row or column interpolating impedances and that these impedances insome circumstances may be defined dynamically in number and/or valueusing MOSFETs or other transconductors. In this exemplary VIA sensorsegment it can be seen that one column (0523) of the array is activelydriven while the remaining two columns (0521, 0525) are held at groundpotential. The rows are configured such that one row (0533) is beingsensed by the signal conditioner (0560)/ADC combination (0550) while theremaining rows (0531, 0535) are held at ground potential.

Simplified Method (0600)

A method associated with the simplified schematic of FIG. 5 (0500) isdepicted in FIG. 6 (0600). Here the column driver, column sources, androw sinks are simplified as depicted in FIG. 5 (0500) with acorresponding reduction in overall method complexity. This simplifiedexemplary present invention method can be generally described in theflowchart of FIG. 6 (0600) as incorporating the following steps:

-   -   (1) The control logic drives one active column electrode at a        time (0601), while grounding all the other active column        electrodes (0602).    -   (2) For each powered drive electrode, the control logic connects        one sense electrode at a time to the conditioning circuit        (0603), while grounding all the other active row electrodes        (0604). This creates multiple possible current paths through the        force sensing elements near the intersection of the powered        drive electrode and the sense electrode, which is connected to        the conditioning circuit. Force applied to the sensor creates a        signal that is proportional to the force and the distance of the        force to the intersection.    -   (3) The signal passes through the conditioning circuit which may        perform current to voltage conversion (0605), optional        filtering, and/or amplification and generates an analog output        signal (0606).    -   (4) The ADC converts the signal output from the signal        conditioning circuitry into a digital value and stores it into        an array in memory (0607). This is repeated for each        intersection (steps (0601)-(0607)) between the active row and        active column electrodes (0608).    -   (5) After the full sensor is scanned, the control circuit may        optionally process the array in memory to further filter the        signal, normalize the signal into known units, extract features        such as touches, and track touches over time (0609).    -   (6) The control circuitry may interact with external components        to exchange data. It may also choose to change scan parameters        in order to optimize for power, speed, or latency for subsequent        scans. It may also respond to a user request or decide to shut        down or sleep between scans (0610).

This general method may be modified heavily depending on a number offactors, with rearrangement and/or addition/deletion of stepsanticipated by the scope of the present invention. Integration of thisand other preferred exemplary embodiment methods in conjunction with avariety of preferred exemplary embodiment systems described herein isanticipated by the overall scope of the present invention.

Exemplary Non-Orthogonal VIA (0700)

As depicted in FIG. 7 (0700), the VIA may be configured in anon-orthogonal configuration in some preferred embodiments with no lossof generality in the invention teachings. This drawing depicts thegeneral concept that a wide variety of VIA sensor element layouts arepossible using the present invention teachings and as such, theinterpolation techniques taught herein are not limited to a particularVIA layout or coordinate system.

Exemplary Radial/Elliptical VIA (0800)

As depicted in FIG. 8 (0800), the VIA may be configured in a radialconfiguration in some preferred embodiments with no loss of generalityin the invention teachings. While the radial configuration depicted iscircularly symmetric with respect to the origin of the VIA, somepreferred invention embodiments as depicted may configure this as anelliptical array by stretching/contracting/rotating one or more axes ofthe VIA array.

Exemplary Voltage-Mode Column Drive Circuitry (0900)-(1100)

While the column drive circuitry may take a wide variety of formsconsistent with the present invention teachings, one exemplary form isgenerally illustrated in FIG. 9 (0900). Here the ACTIVATE COLUMN signal(0910) is presented to an inverter chain (0901, 0902) and then providedwith tri-state connectivity via the transmission gate (0903) to the IICcolumn drive signal (0920) that is connected to the IIC interpolationstructure within the VIA. The transmission gate (0903) is designed toactively couple the output of the inverter chain (0902) to the IICcolumn drive (0920) when the ENABLE SWITCH signal (0930) is active. Thetri-state inverter (0904) provides the necessary signal inversion toensure that the transmission gate (0903) is capable of bidirectionalcurrent flow. Note that the column drive voltage (0940) may be differentthan other voltages supplied to the inverters shown, as the P2 MOSFETmay be configured as a power driver, depending on the column applicationspecific configuration of the inverter chain (0901, 0902).

It should be noted as depicted in FIG. 10 (1000) that other embodimentsof this tri-state switch configuration are possible wherein stackedMOSFET switches may be used in combination to provide for both theactivation and tri-state drive control functions shown in FIG. 9 (0900).In this example, inversion circuitry for the ACTIVATE and ENABLE signalshas been omitted for clarity. The major difference in the embodiment ofFIG. 10 (1000) exists in the requirement for additional headroom voltagerequirements (the supply voltage must be higher) and the use of aunified supply voltage for all switching operations. The configurationof FIG. 9 (0900) is preferable in many applications because dynamicpower consumption associated with switching the VIA will be on the orderofP=½CV ² f  (5)with P representing the dynamic power consumption, C representing thereactive VIA load capacitance, V representing the switched voltagedifferential, and f representing the switching (scanning) frequency.Thus, a reduction in switched voltage across the VIA sensors candrastically reduce the amount of power consumed by the touch sensorscanning operation. By using different driving voltages within theembodiment of FIG. 9 (0900) (i.e., reducing the column drive voltage(0940)), a considerable reduction in overall power consumption can berealized.

The stacked driving approach depicted in FIG. 10 (1000) may be modifiedto form a non-stacked IIC column driver as generally depicted in FIG. 11(1100). Here the addition of logic driving the output CMOS inverterpermits lower overall voltage operation for the system. This logicconfiguration is often incorporated in microcontroller tri-state GPIOcircuitry.

Exemplary Voltage-Mode Row Sense Circuitry (1200)-(1300)

While the row sense circuitry may take a wide variety of formsconsistent with the present invention teachings, one exemplary form isgenerally illustrated in FIG. 12 (1200). Here the IIR row sense signalline (1210) is electrically coupled to the ADC input (1220) via a MOSFETswitched ground shunt (1201) coupled to a transmission gate (1202). Whenthe ENABLE SWITCH signal (1230) is active, the MOSFET shunt (1201) isdisabled and the transmission gate (1202) is activated via inverter(1203), which couples the selected IIR row sense signal line (1210) tothe ADC (1220). When the ENABLE SWITCH signal (1230) is inactive, theMOSFET shunt (1201) is enabled, which grounds the IIR row sense signalline (1210) and disables the transmission gate (1202) which decouplesthe selected IIR row sense signal line (1210) from the ADC (1220).

It should be noted that in some circumstances this switching circuitrymay involve more than simple passive signal switching and mayincorporate active amplification/filtering devices to condition the IIRrow sense signal line (1210) before presentation to the ADC (1220).Implementation of this type of switched active buffering is well withinthe skill of one of ordinary skill in the electrical arts.

The circuitry depicted in FIG. 12 (1200) may be augmented and modifiedas depicted in FIG. 13 (1300) to incorporate a GROUND ENABLE signal(1340) and associated logic gate (1341) to permit optional disablementof IIR row sense line grounding in situations where the row sense lineis not being sensed or grounded such as in multi-resolution scanningoperations. Circuit components (1301, 1302, 1303, 1310, 1320, 1330) inthis embodiment generally correspond to elements (1201, 1202, 1203,1210, 1220, 1230) in FIG. 12 (1200).

Exemplary Current-Mode Column Drive Circuitry (1400)-(1500)

The exemplary voltage-mode column drive circuitry generally depicted inFIG. 9 (0900)-FIG. 12 (1200) may also in some invention embodiments beimplemented using a current-mode approach as generally depicted in FIG.14 (1400) and FIG. 15 (1500). These schematics generally depict astructure and function similar to that of FIG. 9 (0900)-FIG. 12 (1200),but incorporating a current-mode driving approach wherein the P5/P6devices form a current mirror that mirrors current drawn by R1 when N6is activated by the ENABLE signal (1430).

As generally depicted in FIG. 15 (1500), a variety of methods may beused to ground the IIC column lines, either by using a single MOSFET (asa non-ideal current sink), or by using a more conventional currentmirror based current sink. Note that since the current forced in theseconfigurations (1450, 1550) may be “dialed in” using a computercontrolled device (R1) (as generally depicted in FIG. 17 (1700)), thisembodiment may be useful in situations where power consumption must beminimized.

Exemplary Current-Mode Row Sense Circuitry (1600)

The exemplary voltage-mode row sense circuitry generally depicted inFIG. 12 (1200)-FIG. 13 (1300) may also in some invention embodiments beimplemented using a current-mode approach as generally depicted in FIG.16 (1600). This schematic generally depicts a structure similar to thatof FIG. 12 (1200)-FIG. 13 (1300) but incorporating a current-modesensing approach. Here the IIR row sense signal (1610) supplies acurrent that is either shunted by switch N1 (1601) or mirrored (1602) bythe combination of N2, N4, and N5 to supply a sink current that isconverted by the current mode ADC (1620). The ENABLE signal (1630) isused to gate the shunt switch (1601) via inverter (1603) and provide anenable for the current mirror (1602) via N2.

Exemplary Variable Interpolation Resistors (1700)

The impedances interconnecting the individual columns (IIC) and theindividual rows (IIR) may be configured as fixed resistors (possibly ofdifferent values within each column and/or row), but may also beconfigured as variable resistances as by using MOSFETs as linearconductors configured as voltage modulated transmission gates asdepicted in FIG. 17 (1700). Here the DACs may be used to modulate theeffective resistance of the X and/or Y impedance elements under controlof a microcontroller or other computing device. One skilled in the artwill be familiar with a wide variety of DAC hardware implementationsthat are compatible with this design approach.

Active Circuitry Variable Impedance Array Elements (1800)

The variable impedance array (VIA) typically incorporates an impedanceelement that is passively structured, such as a resistor, capacitor,inductor, or other passive device combination involving these primitiveelements. However, some preferred invention embodiments may utilizeactive circuitry associated with the passive VIA component. An exampleof this active circuitry construction is depicted in FIG. 18 (1800)wherein a VIA active sensor element (1810) includes a passive VIA sensorelement (1811) that is augmented with an active circuitry (1812) whichinterlinks a VIA/IIC column (1813) and VIA/IIR row (1814).

One possible exemplary embodiment of this concept is depicted with theVIA active sensor element (1820) comprising a passive VIA sensor element(1821) that is augmented with a MOSFET (1822) that interlinks a VIAcolumn (1823) and row (1824). One skilled in the art will recognize thatthe VIA cell (1811, 1821) may comprise a wide variety of variableimpedance elements, and that the active circuitry (1812, 1822) maycomprise a wide variety of active circuitry consistent with coupling anindividual VIA column (1813, 1823) and VIA row (1814, 1824).

Exemplary Variable Frequency Excitation/Detection (1900)-(2000)

As generally depicted in FIG. 19 (1900), the present invention mayutilize selectable frequency generation within the CSR (1920) to excitethe VIA (1910). While this architecture generally mimics that depictedin FIG. 4 (0400), the addition of a selectable filtering element (1960)permits individual excitation frequencies to be filtered from the VIA(1910) and then detected by the ADC (1950) before being processed by thecontrol logic (1940). In some circumstances, the selectable filteringelement (1960) may be incorporated within the ADC (1950). In thisexample, the CSR (1920) AC excitation may take the form of one or moresingular frequencies or a plurality of frequencies. The use of anarbitrary waveform generator (AWG) in this configuration for thegeneration of the CSR (1920) frequencies is anticipated in someembodiments.

Note that the use of multiple excitation frequencies within the CSR(1920) along with parallel multiple frequency detection by theprogrammable filter (1960) may permit multiple areas of the VIA (1910)to be detected simultaneously. This in conjunction with appropriatecontrol logic (1940) software/firmware can allow multiple touch areas tobe properly detected and also permit the use of varying frequencies todetect finer registration within the VIA (1910). This multi-frequencyapproach may also be used in some circumstances to reduce the powerrequired to operate the touch sensor detector system.

An example of this multi-area frequency-based scanning approach isdepicted in FIG. 20 (2000) wherein the VIA is excited with variousfrequencies along the columns, and by selective filtering of frequencyinformation on the row sensors, the VIA can be sensed based on frequencyin addition to variations in individual VIA sensor element impedance.Note that this may in some circumstances permit multiple areas of theVIA surface to be associated with different sensing mechanisms, such aspressure, proximity, interaction with a capacitively coupled stylus,etc.

Variable Scan Resolutions (2100)-(2400)

The present invention anticipates that by varying the IIC columnexcitation and IIR row sensing IIR configurations, that a variety ofscanning resolutions may be obtained from a given invention embodiment.Several examples of this variable scan resolution capability areillustrated in FIG. 21 (2100)-FIG. 24 (2400). In these examples, thesolid horizontal/vertical lines represent active rows/columns in theVIA, and the dashed lines represent interpolated rows/columns within theVIA. Each row/column may be considered in either an active state(columns are driven/grounded and rows are sensed/grounded) or in adisconnected state (high impedance state).

FIG. 21 (2100) illustrates a scenario in which a full resolution scan isconfigured and all columns are driven and all rows are sensed during ascan. A half resolution scan is depicted in FIG. 22 (2200) wherein everyother row/column is connected and driven/sensed during a scan. Aquarter-resolution scan is depicted in FIG. 23 (2300) wherein everyfourth row/column is connected and driven/sensed during a scan. Finally,FIG. 24 (2400) illustrates the concept of a mixed-mode scan in which aportion of the VIA is scanned at full resolution and the remainingportion of the VIA is scanned at a lower resolution. The ability to varyscan resolutions greatly aids in power conservation for the overalltouch sensor system by reducing the dynamic power loss associated withscanning each column/row of the VIA. One skilled in the art willrecognize that the example of FIG. 24 (2400) may be configured toperform a full resolution scan at a number of discrete areas within theoverall VIA structure.

Pen/Stylus Embodiment (2500)-(3200)

Overview (2500)

As generally depicted in FIG. 25 (2500)-FIG. 32 (3200), the presentinvention may incorporate the use of a user (2501) pen/stylus (2520) asa GUI (2502) input in addition to the touch sensor detector. As depictedin the block diagram of FIG. 25 (2500), this alternate embodimentprovides for similar functionality as depicted in FIG. 1 (0100), butwith the addition of a pen/stylus (2520) that may communicate with thetouch sensor detector (TSD)/touch sensor array (TSA) (2510) and/or thecomputer system (2503) under control of machine instructions read from acomputer readable medium (2504).

Active Capacitive Stylus (2600)

As generally depicted in FIG. 26 (2600), the use of an active capacitivestylus (2620) in this configuration permits the stylus (2620) to emit asignal (such as a selected AC frequency) (2621) that is then detected bythe TSA (2610) and used in a one-dimensional scanning approach todetermine the X and Y positions of the stylus separately. As depicted inthis diagram, the computer system (2601) may be configured to wirelesslycommunicate (2602) with the TSA (2610) as well as wirelessly communicate(2603) with the stylus (2620) in this configuration.

As depicted in the diagram, in some circumstances the active capacitivestylus (2620) may be configured to receive wireless transmissions (2622)from an individual VIA sensor element (2623) and communicate thisinformation to the computer system (2601) wirelessly. In this fashionthe VIA may be used to communicate information (location, pressure,detected capacitance, proximity, etc.) to the stylus (2620) which isthen relayed to the computer system (2601).

Exemplary Stylus Schematic (2700)

A block diagram schematic of an exemplary active capacitive stylus isdepicted in FIG. 27 (2700), wherein a power source (typically a 1.5Vbattery) (2701) is boost converted by a power control module (2702)under control of a low power microcontroller (2703) to supply power tothe system. The microcontroller operates to control an oscillator (2704)that drives a PCB antenna (2705) with signals designed for reception bythe TSA after transmission by the stylus tip (2706). Radiation couplingbetween the oscillator (2704) and stylus tip (2706) is typicallycapacitive but may be aided by the on-board PCB antenna (2705). The typeof signal emitted by the oscillator (2704) may be controlled by themicrocontroller (2703) in some circumstances by optional user input(2707) that may take the form of a TSA within the stylus body, oroptional keyboard switches or capacitive sensors contained within thestylus body. This user input (2707) may put the stylus into differentmodes of operation that convey distinct information to the TSA throughthe stylus tip (2706). Thus, the stylus tip (2706) may conveyinformation such as pressure/location to the TSA, but also provide modeindicators based on the state of the oscillator (2704) output.

In conjunction with the stylus (2706) communication modes to the TSA,the stylus may also be configured with a wireless interface (WiFi,BLUETOOTH®, etc.) that may make use of the oscillator (2704) and/or PCBantenna (2705) to communicate with the TSA electronics and/or thecomputing device to which the TSA electronics communicates as depictedin FIG. 26 (2600).

Exemplary Stylus Construction (2800)-(2900)

Exemplary stylus construction details are provided in FIG. 28(2800)-FIG. 29 (2900) wherein the stylus comprises top (2801) and bottom(2802) enclosure shells that are configured with mating threads (2803)for assembly. Within this two-piece shell structure, a battery (2804)supplying power and PCB (2805) containing the active electronics arecontained along with a stylus tip (2806) that is designed to makecontact with the protective cover overlaying the TSA. An optionalmechanical switch (2807) may be included to support power control to thestylus or as a means of changing operating modes of the stylus. Springs(2808, 2809) may be included to affect battery (2804) contact as well aspermit the stylus tip (2806) to freely move when placed in contact witha flat surface such as that of the TSA protective cover.

Associated with the microcontroller (2703) in the stylus there may alsobe a variety of user input mechanisms (such as switches or other inputs)(2807) that may allow modification of the operating modes of the stylus.An example of this is illustrated in FIG. 28 (2800) wherein bands (2811,2812, 2813, 2814, 2815) on the outer surface of the bottom enclosureshell (2802) are sensed by capacitive coupling to determine user switchinputs to the microcontroller and thus set the operating mode of thestylus. While other mode selection methods are possible, this is justone example of the ability of the stylus to operate in a variety ofmodes with the TSA.

FIG. 29 (2900) provides additional detail on the internal constructionof the stylus, including the PCB, spring loaded contacts to the stylustip, and provision for PCB trace antennas to aid in both communicationwith the TSA and/or a computing system using the TSA as an input device.

Exemplary Input Data Profiles (3000)-(3200)

As depicted in FIG. 30 (3000)-FIG. 32 (3200), the present invention mayintegrate the use of hand/finger gestures on a tablet surface (3110,3210) as well as pen/stylus input to produce pressure/presence profiles(3120, 3220) as depicted in FIG. 31 (3100) and FIG. 32 (3200). Asdepicted in FIG. 30 (3000), the system may be used to collect pressureinformation from various user fingers (or other parts of the user hand)as well as the stylus/pen input. As depicted in FIG. 31 (3100), theseinputs may form a pressure map in which each hand/finger/stylus input isassociated with a pressure profile in the TSA. These pressure profilescan be distinguished as coming from the user hand/fingers (P) or thestylus (S) as depicted in FIG. 32 (3200), because the stylus in thisinstance is an active capacitance stylus as previously discussed and isemitting wireless information to the TSA during operation. Note that inFIG. 32 (3200) the system may be configured to distinguish betweenpressure inputs (defined as ellipses in these diagrams) (P) as comparedto stylus inputs (S), thus permitting a different dimensional plane ofinputs to the same TSA. This additional plane of information may be usedby application software running on the remote computer system to affecta variety of operating modes or controls within the applicationsoftware.

Detailed Description—IFSA Embodiment (3300)-(6400) Overview

While the present invention may be implemented using a wide variety ofsensor technologies in the VIA, one preferred collection of exemplaryembodiments utilize pressure-sensitive sensors to form an interpolatingforce sensing array (IFSA). The following discussion details thispressure-sensitive class of preferred embodiments and provides detailedexemplary construction contexts. Note that while the IFSA embodimentsare detailed below, the techniques used in their construction may beequally applied to other types of sensor technologies such ascapacitive, electromagnetic, etc.

In accordance with the above general description, the present inventionIFSA embodiment describes systems and methods for constructing a highresolution force sensing array, an interpolating circuit that allows thedrive and sense circuitry to have a lower resolution than the forcesensing array, a circuit and accompanying algorithms for scanning thesensor and processing the resulting signals, and methods ofincorporating this sensor into various devices.

An IFSA sensor typically consists of the following components. Furtherdetail and clarification on each component can be found in the detaileddescription which follows.

-   -   Sensing Area. A sensing area consisting of row and column        electrodes and a grid of force sensing elements where each        element is connected between one row and one column electrode.    -   Interpolation Resistors. A series of interpolation resistors        connecting to the column and row electrodes and the drive/sense        circuit.    -   Drive Circuit. A drive circuit, which consist of a series of        digital and/or analog switches and associated control logic        attached to the active columns.    -   Sense Circuit. A sense circuit, which consist of a series of        digital and analog switches and associated control logic        attached to the active rows.    -   Voltage/Current Source. A voltage or current source, which        provides drive voltage/current to the drive circuit.    -   Signal Conditioning. An optional signal conditioning component,        which conditions, filters, or transforms the signal coming out        of the sense circuit.    -   Control Circuit. A control circuit, typically a microcontroller        or ASIC, which generates the sequence of control signals        necessary to scan a sensor. The control circuit may also        incorporate an internal or external ADC for conversion of sensor        signals from analog to digital format, a processor and memory to        process and interpret the signals, and IO logic to communicate        with external components, such as a host processor.

Note that the rows and columns in the circuit may be interchanged, butfor the purposes of illustration, the present invention connects thedrive circuit to the columns and the sense circuit to the rows. Alsonote that the components are shown separately for the purposes ofillustration. The functions of these components may be merged and/orseparated in an actual implementation. Some examples of this wouldinclude merging the interpolation resistors with the sensing area,incorporating the voltage source into the drive circuitry, placing theADC external to the control circuit, etc. For clarity, the presentinvention calls the column and row electrodes that directly connect tothe drive and sense circuitry active column and active row electrodes,while those that connect to the drive and sense circuits through theinterpolation resistors are called interpolating column and rowselectrodes.

During operation, the control circuit repeatedly scans the sensor toretrieve two dimensional “images” of the force distribution on thesensor. Each scan cycle is called a frame. Below is an overview of thesteps that happen during each frame. Further detail and clarification oneach step can be found in the detailed description.

-   -   (1) The control logic drives one active column electrode at a        time, while grounding all the other active column electrodes.    -   (2) For each powered drive electrode, the control logic connects        one sense electrode at a time to the conditioning circuit, while        grounding all the other active row electrodes. This creates        multiple possible current paths through the force sensing        elements near the intersection of the powered drive electrode        and the sense electrode which is connected to the conditioning        circuit. Force applied to the sensor creates a signal that is        proportional to the force and the distance of the force to the        intersection.    -   (3) The signal passes through the conditioning circuit which may        perform current to voltage conversion, filtering, and/or        amplification, and generates an analog output signal.    -   (4) The ADC converts the signal output from the signal        conditioning circuitry into a digital value and stores it into        an array in memory. This is repeated for each intersection        between the active row and active column electrodes.    -   (5) After the full sensor is scanned, the control circuit may        process the array in memory to further filter the signal,        normalize the signal into known units, extract features such as        touches, and track touches over time.    -   (6) The control circuitry may interact with external components        to exchange data. It may also choose to change scan parameters        in order to optimize for power, speed, or latency for subsequent        scans. It may also respond to a user request or decide to shut        down or sleep between scans.    -   (7) The signals sent out to external circuitry are used by        hardware and/or software specific to the product in which IFSA        is used to perform the desired task.

The components and processes described work in concert to enable thesensor to capture pressure distributions, process the data, and outputmeaningful information to enable a wide variety of applications. Theforegoing purposes, features, and advantages of the invention as well asthe detailed design, implementation, and manufacturing of the inventionare clarified and discussed in more detail in the detailed descriptionof the invention provided herein.

Theory of Operation (3300)-(3600)

Introduction

The following discussion will describe on a conceptual level how an IFSAsensor is constructed and how that construction enables interpolation.As described earlier, an IFSA sensor has a set of active row and columnelectrodes, which are connected to the drive and sense circuitry. Inbetween each pair of active row and column electrodes, there are one ormore interpolating electrodes. Although the number of interpolatingelectrodes between each row and column pair can vary, most IFSA sensordesigns will keep this number constant and reference it as the number N.

FIG. 33 (3300) depicts an example of an IFSA circuit with four activecolumn electrodes, five active row electrodes, and two interpolatingelectrodes between each pair of column and row electrodes. Thus, withcircuitry that would normally only be able to read a 4×5 sensor, thepresent invention is able to read forces from a 10×13 array of forcesensing elements. With this arrangement, the present invention hastripled the effective tracking resolution of the sensor in both X and Ydimensions compared to the number of rows and columns that are hooked upto the readout electronics. Furthermore, by increasing the number N ofinterpolating row and column electrodes, the present invention canfurther increase the tracking resolution of the sensor, with the onlylimit being the capability of the manufacturing process used to createthe sensor.

Force Sensing Elements

At the intersection of each pair of row and column electrodes is a forcesensing element, represented in the present invention schematic as avariable resistor. A variety of different materials, configurations, andmanufacturing methods can be used to create the force sensing elements,which are described in a later section. Most force sensing elements thatwould be used in IFSA sensors respond in a similar fashion to appliedforce—as force is applied, the resistance decreases. However, therelationship between resistance and force is typically non-linear. Forthis reason, rather than measuring resistance, it is preferable tomeasure the conductance of a sensor, which is the inverse of theresistance. As pressure is applied, the conductance increases in alinear or near-linear fashion. If the constant of proportionality (whichcorresponds to sensitivity) is assigned the variable k, the amount offorce applied at a particular sensor element F, and the conductivity ofthe sensor element C, then the present invention can model theconductivity C of the sensor with respect to force F with the followingequation:C=kF  (6)If a voltage is applied across the force sensing element, Ohm's lawstates that the amount of current I that will flow through the forcesensing element will be proportional to the force times the voltage V:I=kFV  (7)Interpolating Resistors

Connected in between each pair of neighboring electrodes (both activeand interpolating) is an interpolation resistor. Although some sensorembodiments may have varying values for the resistance values of theinterpolating resistors, for the sake of this example, assume that allthe interpolating resistors have the same resistance value Ri. Theseresistors form a series of resistive divider circuits which, as shall beseen, enable the interpolating property of the sensor.

Interpolation in Action

Activity that occurs when the present invention scans an intersection ofthe IFSA sensor is detailed as follows. At any point in the scan of asensor, one active column electrode is driven to a known voltage Vd,while its neighboring column electrodes are connected to ground.Simultaneously, the current Is flowing out of one active row electrodeis measured while neighboring row electrodes are connected to ground. Asmentioned earlier, the number of interpolating electrodes between agiven pair of active column or row electrodes can vary across thesensor, but for the purposes of illustration, assume that the presentinvention sensor embodiment is constructed with a consistent number ofinterpolating electrodes between each pair of active column and rowelectrodes. This number is referenced herein as N.

When the voltage Vd is applied by the drive electronics, each forcesensing element in the area between the two grounded column electrodesand the two grounded row electrodes contributes some current to thetotal sensed output current Is in a fashion that is linear with respectto the force on the element and the distance from the row-columnintersection. To understand how each of these force sensing elementscontributes to the final output value, reference FIG. 34 (3400), whichdepicts a subsection of an IFSA sensor (such as the sensor in FIG. 33(3300)) during the moment in time of a sensor scan where the row/columnintersection at the center of the diagram is being scanned. This sensorhas two interpolating electrodes between each pair of active row andcolumn electrodes (N=2). In this figure, the present invention assignseach column electrode (whether it is active or interpolating) an xcoordinate based on its distance from the current powered electrode(which is column electrode 0 in this example). In this figure, theleftmost, central, and rightmost electrodes are active electrodes. Theyare numbered −3, 0, and 3, respectively (for a general sensor with adifferent N, they would be numbered −(N+1), 0 and (N+1)). In betweenthem are two groups of interpolating electrodes. These electrodes arenumbered −2 and −1 (−N through −1 generally) and 1 and 2 (1 through Ngenerally). We assign each row electrode a y coordinate based on itsdistance from the currently sensed electrode (which is row electrode 0in this example) in a similar fashion. Finally, the present inventionassigns a coordinate of (X, Y) to each force sensing element at theintersection of column X and row Y.

Remember that all the neighboring column and row electrodes around thedriven and sensed electrode are driven to ground. Thus, columnelectrodes −3 and 3 are grounded, and so are row electrodes −3 and 3. Inthe remainder of this section, the present invention shows that thissets up a distribution of sensitivity around the intersection of column0 and row 0, which falls off in a linear fashion along both X and Ydirections.

On the drive side, the set of interpolating resistors which interconnectthe interpolating electrodes in between the driven active electrode andthe neighboring active electrodes, which are grounded, form a series ofvoltage dividers. These resistors all have the same resistance value ofRi. Thus, the present invention can express the voltage at each of thesecolumn electrodes Vc as a function of x as:

$\begin{matrix}{{V_{c}(x)} = {V_{d}\left\lbrack \frac{\left( {N + 1 - {❘x❘}} \right)}{N + 1} \right\rbrack}} & (8)\end{matrix}$

Between each row and column electrode is a force sensing element asdescribed earlier. The current flow through the force sensing elementvaries in proportion to the applied force and the applied voltage. If agiven column electrode is at a voltage of Vc(X) as described above, theconstant of proportionality of the force sensing element is k, and ifthe present invention assumes that the sense side of the force sensingelement is at a potential of 0 volts (it will be described later whythis is a reasonable assumption), the current If(X,Y) that flows throughthe force sensing element at location (X,Y) is:I _(f(x,y)) =V _(c)(x)×kF _((x,y))  (9)

On the readout side, the interpolating resistors in between each pair ofactive electrodes also act as a series of resistive dividers, except inthis case, they split the current flowing into an electrode through theforce sensing element between the neighboring active electrodes, whichare both at ground potential. In this example, one of these electrodesis being sensed and the neighboring active electrode is being grounded.The contribution to the current at the active sense electrode from forcesensing element (X,Y) can be expressed as:

$\begin{matrix}{I_{C({x,y})} = {I_{f({x,y})}\left\lbrack \frac{\left( {N + 1 - {❘y❘}} \right)}{N + 1} \right\rbrack}} & (10)\end{matrix}$Now, substituting the equation for If(X,Y) into the equation above, andthen substituting the equation for Vc(X) into the resulting equation,the following equation is produced for Ic(X,Y):

$\begin{matrix}{I_{C({x,y})} = {kF_{({x,y})} \times {V_{d}\left\lbrack \frac{\left( {N + 1 - {❘x❘}} \right)}{N + 1} \right\rbrack} \times \left\lbrack \frac{\left( {N + 1 - {❘y❘}} \right)}{N + 1} \right\rbrack}} & (11)\end{matrix}$Because k, Vd, and N are all constant, it is seen that the contributionto the output current that is read out from the intersection of anactive row and column electrode is proportional to the force F(X,Y)applied to location (X,Y) and the distance in X and Y of the forcesensing element from the row-column intersection.

Because the voltage divider circuit between the columns and the currentdivider between the rows both behave linearly, the current contributionfrom each sensing element is additive, so the final sensed current Isfor a given row-column intersection can be expressed as:

$\begin{matrix}{I_{s} = {\frac{kV}{\left( {N + 1} \right)^{2}}{\sum\limits_{x = {- N}}^{+ N}{\sum\limits_{y = {- N}}^{+ N}{{F_{{({x,y})}^{\times}}\left( {N + 1 - {❘x❘}} \right)} \times \left( {N + 1 - {❘y❘}} \right)}}}}} & (12)\end{matrix}$

This formula models how each row/column intersection behaves withrespect to a distribution of forces applied to the sensing elementsaround that intersection (note that there is some nonlinearity that isnot modeled by this formula, but the effects are typically negligible,as described later). To understand what is happening more clearly, thepresent invention can compute the percent contribution that each sensingelement contributes relative to the element at (0,0) to a reading at theintersection of an active row and column. We calculate this for each ofthe 49 force sensing elements at each row/column intersection of thesensor in FIG. 34 (3400). FIG. 35 (3500) depicts the results of thesecalculations, which are the relative contributions of the 7×7 array offorce sensing elements depicted in FIG. 34 (3400). This sensitivitydistribution is visualized in three dimensions in FIG. 36 (3600).

Because the same distribution happens at every scanned intersection ofan active row and column, each sensing element contributes its signal tothe active row/column electrode intersections around it in a fashionthat is linearly related to its distance from those intersections.Because the falloff of the contributions in X and Y is linear, thepresent invention can use linear interpolation, applied to the array offorce values read out from each intersection of an active row and columnto accurately calculate the centroid of a force distribution applied tothe sensor.

Furthermore, the resolution with which the present invention can trackthat centroid is proportional not to the resolution of the activesensing lines, but to the resolution of the interpolating lines. Thus,simply by increasing N, the present invention can increase the trackingresolution of the present invention sensor.

Non-Linearity Due to Current Flow Through Force Sensing Element

In deriving the equations above, the effect of current flow through theforce sensing element was not taken into account. This current causes adrop in the voltage Vc at the drive side of the force sensing elementand an increase in the voltage at the sense side of the force sensingelement above ground potential. Thus, less current than predicted by theequations will flow through the sensor, yielding a slightly reducedsensitivity.

More problematic is that the resulting current flow through theinterpolating resistors skews their voltages and affects the response ofother nearby force sensing elements. Fortunately, this problem can bemitigated by picking low resistance values for the interpolatingresistors and designing the force sensing elements to have significantlyhigher resistance values in their useful operating range. This ensuresthat the scale of this effect is relatively small and does notsignificantly affect the accuracy of the sensor. Beneficially,increasing the resistance of the force sensing elements also reducesoverall power consumption.

Force Sensing Calculations

Overview

A variety of preferred invention embodiments utilize apressure-sensitive array as part of the VIA structure. Within thisapplication context, a variety of force calculations may be incorporatedwithin the control logic in conjunction with the overall interpolationfunction that is applied across multiple columns and rows of the VIA.The following discusses these calculations in detail and provides areference point for implementation of a wide range of inventionembodiments utilizing this form of VIA structure as the basis of theinterpolation process.

The force and position of a touch are computed with arithmeticoperations on the two-dimensional array of sensor values read out from asensor. In a force sensing sensor, the sensor values correspond toforce, and in a capacitive sensor, they may correspond to a capacitivesignal. These calculations are generally known to those familiar withsignal processing for touch sensors.

While the present invention cannot reconstruct the forces on theindividual sensor elements after doing a scan at a lower resolution(such as the active electrode resolution), the present invention canreconstruct higher-order information such as the force and position of atouch at the full resolution (such as the VIA resolution) of the sensor.Several reasons that the present invention achieves this result are asfollows:

-   -   the interpolation network allows the sensor to be downsampled in        a linear fashion; and    -   the computational methods used to compute force and position of        a touch are linear in nature.

The THEORY OF OPERATION section above described the first capability byshowing mathematically that the present invention approach creates alinear downsampling of the sensor signal. The remainder of this sectionwill explain the second aspect by providing more detail on the methodsused to compute the force and position of a touch.

Because the downsampling is happening in hardware and the math used forthe calculation are both linear, the accuracy that the present inventiongets from scanning the sensor at a lower resolution is the same as ifthe present invention were to scan it at the full resolution of thesensor elements. Furthermore, this is also true no matter how small orhow big a touch is (whether it covers a single sensor element or manysensor elements). The only thing the present invention loses is theability to distinguish two touches that are closer together than the“Nyquist period” of the present invention scan.

This is important because it means that the present invention can senseat a high resolution, using low resolution scan electronics, withoutsacrificing accuracy. Or, the present invention can boost the accuracyof a low resolution sensor without introducing extra electronics.

The only calculation that is not mathematically preserved is the area(because after interpolation, there is no way to tell exactly how manysensor elements were activated). However, this generally is not aproblem since there are ways to approximate the area calculation.

While it is possible to use a method such as spline interpolation toapproximately reconstruct the force values sensed by each of the sensorelements, the present invention may not opt to do this in firmware. Thereason is that this would be very computationally expensive and would inmany ways defeat the benefits of scanning the sensor at a lowerresolution. Instead, the present invention typically performs the mathdescribed below on the low resolution scan image and because of thelinearity property, the present invention achieves the same result as ifit had done the math on the full resolution scan image.

Note that some preferred invention embodiments may up-sample thetwo-dimensional force array in firmware to better estimate the positionof the touch, or to implement multi-resolution scanning. However, on thePC side, the present invention may utilize spline interpolation toup-sample the low-resolution force image back to the resolution of thesensor elements for the purpose of achieving aesthetic visualization ofthe VIA data. The following is a summary of how the present inventioncalculates the force and position of a touch.

Calculating Force of a Touch

The force of a touch is the sum of all force values of the touch. Notethat in this section, mathematical operations on the TSM data read outfrom the sensor are being described. N, X and Y refer to the dimensionsof the TSM matrix and the (X,Y) coordinates of the data in the matrix,and F(X,Y) refers to data at coordinate (X,Y) in the TSM. They do NOTrefer to interpolating electrodes.

$\begin{matrix}{{TotalForce} = {\sum\limits_{x = 0}^{N}{\sum\limits_{y = 0}^{N}F_{({x,y})}}}} & (13)\end{matrix}$The total force is referred to as F_(total) in this application.Calculating the Touch Position

The position of a touch in the X dimension is the force-weighted averageof the X positions of the touch. Similarly, the position of a touch inthe Y dimension is the force-weighted average of the Y positions of thetouch.

$\begin{matrix}{X_{Position} = {\frac{1}{F_{total}}{\sum\limits_{x = 0}^{N}{\sum\limits_{y = 0}^{N}{xF_{({x,y})}}}}}} & (14)\end{matrix}$ $\begin{matrix}{Y_{Position} = {\frac{1}{F_{total}}{\sum\limits_{x = 0}^{N}{\sum\limits_{y = 0}^{N}{yF_{({x,y})}}}}}} & (15)\end{matrix}$The X and Y positions are referred to as μ_(x) and μ_(y) in theremainder of the document.Calculating the Touch Shape

The shape of a touch is estimated with an ellipse that surrounds thetouch. The calculation of the ellipse is similar to the calculation ofthe standard deviation of a Gaussian distribution of values, except thatit is performed in two dimensions. The calculation starts by computing a2×2 covariance matrix:

$\begin{matrix}\begin{bmatrix}{XX} & {XY} \\{XY} & {YY}\end{bmatrix} & (16)\end{matrix}$

In this matrix, XX, YY, and XY are the variances of the matrix along X,Y, and the XY diagonal. From this matrix, it is possible to computeeigenvectors, which determine the major and minor axes of the matrix,and eigenvalues, which determine the length of the major and minor axes.

$\begin{matrix}{{XX} = {\frac{1}{F_{total}}{\sum\limits_{x = 0}^{N}{\sum\limits_{y = 0}^{N}{x{F_{({x,y})}\left( {x - \mu_{x}} \right)}^{2}}}}}} & (17)\end{matrix}$ $\begin{matrix}{{YY} = {\frac{1}{F_{total}}{\sum\limits_{x = 0}^{N}{\sum\limits_{y = 0}^{N}{F_{({x,y})}\left( {y - \mu_{y}} \right)}^{2}}}}} & (18)\end{matrix}$ $\begin{matrix}{{XY} = {\frac{1}{F_{total}}{\sum\limits_{x = 0}^{N}{\sum\limits_{y = 0}^{N}{{F_{({x,y})}\left( {x - \mu_{x}} \right)}\left( {y - \mu_{y}} \right)}}}}} & (19)\end{matrix}$

From here, the eigenvectors and eigenvalues of the covariance matrix canbe found using simple mathematics which can be found in any linearalgebra textbook. What is important to note, is that the length of themajor and minor axes can be computed by taking a square root of thefirst and second eigenvalues and multiplying by a factor. This factordetermines what percentage of the touch will be surrounded by theellipse (a factor between 2 and 3 is typically used to surround 95% to99% of the ellipse along X and Y dimensions).

The square root in the calculation results in an approximately linearrelationship between the input to this algorithm and the output values,preserving the benefit of the linear behavior of the present inventionsensor. Finally, the lengths of the major and minor axes can bemultiplied together to estimate area.

As illustrated above, the math used to compute the force, position, andshape of a touch is not affected by the level of interpolation appliedto the sensor.

Multiple Touches

When there are multiple touches, a watershed algorithm is used tosegment the area of the sensor into separate regions, each regioncontaining a single touch. Abstractly, the algorithms described aboveare performed separately on each region to compute statistics for eachtouch.

Touch Area Calculation

The area of a touch is just the number of force values greater than acertain threshold, t.

$\begin{matrix}{{Area} = {\sum\limits_{x = 0}^{N}{\sum\limits_{y = 0}^{N}\left\{ \begin{matrix}\left. {F_{({x,y})} > t}\Rightarrow 1 \right. \\\left. {else}\Rightarrow 0 \right.\end{matrix} \right.}}} & (20)\end{matrix}$The area of a touch will be affected by the level of interpolation sincethe number of readings that are greater than a threshold will decreaseas the level of interpolation increases. This primarily affects toucheswith a small area, for which not enough data points are available toreconstruct the touch area accurately. To ameliorate this, a calculationwhich that is herein termed “soft area” may be used, which uses a softcutoff instead of a hard threshold for t. This provides a betterestimate for area than the calculation above. In general, the area of atouch is not as important to user interface applications as force andposition, thus the decrease in the accuracy of area calculations as aresult of downsampling is acceptable to users.Summary of Benefits

To summarize, the benefits of the present invention approach to pressuresensing can be viewed in two different ways:

-   -   For a sensor design that is starting out with a high resolution        sensor, the present invention approach allows the sensor to be        scanned with lower resolution electronics, while preserving the        accuracy of the calculations of (X,Y) position, force, and        shape. In this case, the cost, complexity, and power consumption        of the system is reduced without sacrificing touch-tracking        performance.    -   Another way to view the present invention approach is for a        design that is starting with a low resolution sensor. In this        case, the present invention approach allows the resolution of        the sensor to be increased while keeping the resolution of the        sensing electronics the same. Thus, the accuracy of the sensor        is improved, without increasing the cost, complexity, and power        consumption of the electronics.

Construction Details (3700)-(5800)

Force Sensing Materials

There is a variety of different materials that can be used to create aforce sensing material (FSM). These include conductive rubber,conductive foam, conductive plastic (such as KAPTON®), and conductiveink. These materials are usually made by mixing conductive particlessuch as carbon particles with insulating particles such as a polymer.The conductive particles can include things such as metal particles(which include silver, gold, and nickel), and materials such asgraphene, carbon nanotubes, silver nanowires, and organic conductors.

Transparent FSMs can be created as well by mixing a transparentconductive material into a transparent nonconductive carrier.Transparent conductive materials include indium tin oxide (ITO),transparent organic conductive particles, or a material that is toosmall to see, such as graphene, carbon nanotubes, silver nanowires, ormetal nanoparticles (which include silver, gold, and nickel).Transparent non-conductive materials for making transparent FSMs includePET, Polyimide, Polycarbonate, or a transparent rubber such as silicone.Alternately, the transparent conductive materials can be deposited ontothe surface of a transparent substrate such as a polymer, glass, orultra-thin flexible glass.

What these materials have in common is a high bulk resistance (at alevel between a conductor and insulator), a rough surface (at amicroscopic scale), and some amount of flexibility. As a result, whenthe material contacts a conductor, the resistance at the interface willdecrease as the force pushing the force sensing material against theconductor is increased.

Some of these materials may also experience a change in bulk resistanceas force is applied as a result of conductive particles coming closertogether. However, this effect is typically small compared to the changein surface resistance. For the purposes of this disclosure, the presentinvention will call all materials with the properties described aboveforce sensing material (FSM), and the present invention shall call thelayer which contains/carries the force sensing material a force sensinglayer (FSL).

Force Sensing Element

Between each row/column electrode intersection is a force sensingelement which creates a variable resistance. There are several differentconfigurations possible for force sensing elements as depicted in FIG.37 (3700)-FIG. 40 (4000). The two most common configurations are whatthe present invention call shunt-mode and thru-mode.

In the shunt-mode configuration, there are two substrates. The topsubstrate is coated with FSM, while the bottom substrate consists of twoelectrodes (FIG. 37 (3700)). As the two substrates are squeezedtogether, the FSM allows current to flow between the two electrodes,causing a variable drop in resistance. In essence, the FSM acts as ashunt between two electrodes. To increase sensitivity, the twoelectrodes can be patterned to form a set of inter-digitated conductivefingers.

The second common configuration is called thru-mode, where the twoelectrodes are patterned onto two separate substrates, and the FSM isbetween them. There are three variants of this configuration. We callthe first variant double-sided thru-mode. In this configuration theelectrodes on the top and bottom substrate are coated with FSM (FIG. 38(3800)). A force sensitive interface is formed between the two layers ofFSM. Squeezing the two layers together causes a variable drop inresistance.

The single-sided thru-mode variant is similar to the double-sidedthru-mode, except only one of the two electrodes is coated with FSM(FIG. 39 (3900)). Typically, it does not matter which of the twoelectrodes, the top or the bottom, is coated with FSM. The final variantis called the sandwich thru-mode. In this variant, the FSM is notdeposited onto the electrodes.

Instead, it forms a layer in between the two electrodes (FIG. 40(4000)). Thus, there are two force sensing interfaces formed between thetop electrode and the FSM, and between the bottom electrode and the FSM.However, from the perspective of the sensor circuitry, these two forcesensing elements act the same as a single force sensing element.

Force Sensing Array Construction (3700)-(4000)

IFSA Sensors are generally constructed as a two-dimensional array offorce sensing elements at the intersection of a set of column and rowelectrodes. Interpolating resistors are connected between each pair ofadjacent column electrodes and each pair of adjacent row electrodes. Theactive column and row electrodes are then connected to the drive andsense circuitry (FIG. 33 (3300)).

The sensor elements can be built using a variety of different thru-modeor shunt-mode configurations (FIG. 37 (3700)-FIG. 40 (4000)). Because asensor array has many sensor elements near to each other, it may benecessary to electrically isolate the sensor elements so that a signalgenerated at one element has a minimal effect on neighboring elements.

The differences between the possible sensor configurations are primarilyin the shape of the electrodes, the way that the force sensing materialis applied over or between the electrodes, and the way that the forcesensing material is patterned to avoid/reduce interaction between nearbysensor elements. The choice of the sensor element design has an impacton the overall sensor construction and vice versa.

Thru-Mode Configurations (4100)-(4300)

Some possible thru-mode configurations are depicted in FIG. 41(4100)-FIG. 43 (4300)). The array in FIG. 41 (4100) is built with thesandwich thru-mode configuration, where the force sensing layer issandwiched between two substrates which carry the row and columnelectrodes which face inwards towards the force sensing layer. A forcesensing element is formed at each intersection of row and columnelectrodes. In these figures, the force sensing material is segmented sothat each force sensing element has its own electrically isolated patchof force sensing material. FIG. 43 (4300) depicts an alternatearrangement where a very thin layer of contiguous force sensing materialis sandwiched between the row and column electrodes. Alternatively, amaterial with a pattern (FIG. 48 (4800)) or pseudo-random pattern (FIG.49 (4900)) of force sensing material can be sandwiched between the rowand column electrodes depicted in FIG. 43 (4300). The array in FIG. 42(4200) is built with the doubled-sided thru-mode configuration, whereeach row and column electrode is coated with force sensing material. Onepossible variation of this (which is not shown) is to coat only the topelectrodes or only the bottom electrodes with force sensing material.

Shunt-Mode Configurations (5000)-(5700)

Some possible shunt-mode configurations are depicted in FIG. 50(5000)-FIG. 57 (5700). All of these configurations consist of adouble-sided circuit board with exposed electrodes on the top side and aforce sensing layer that is placed on top of the exposed electrodes. Inthe shunt mode-configuration, the column and row electrodes cannot bothcompletely reside in the same layer because they would intersect andelectrically short with each other. To address this issue, in theseexamples, the row electrodes are interconnected with horizontal traceson the back of the PCB. The traces on the back can be seen in FIG. 52(5200), FIG. 55 (5500), and FIG. 57 (5700). Vias are used to connectbetween the resulting “pads” on the front of the PCB to the traces onthe back. This collocates a portion of each row electrode with eachcolumn electrode on the front surface, creating the two electricalterminals of the shunt-mode force sensing element. As a result, an arrayof sensor elements is formed by the pattern of electrodes on the uppersurface of the circuit board and the layer of force sensitive materialthat comes down on top of the pattern. A variety of force sensingmaterials and patterns of FSM may be used to create the force sensinglayer as described later. Also, the electrode patterns themselves can bevaried as shown in FIG. 50 (5000)-FIG. 57 (5700).

FIG. 50 (5000) illustrates a simple pattern where each sensing elementconsists of two rectangular areas of exposed conductor (the forcesensing layer is cut away to show the conductor pattern and thealignment of the patches of force sensing material to the pattern). FIG.51 (5100) is a variant of this, where inter-digitating fingers are addedto the two rectangular areas to increase sensitivity of each forcesensing element. FIG. 52 (5200) depicts the pattern of row conductors onthe back side of these two designs. FIG. 53 (5300) illustrates a variantof FIG. 50 (5000) where every other sensor element is flippedhorizontally. This has the effect of halving the number of viasnecessary to create the circuit and increasing the space between vias,which reduces manufacturing cost and can help to increase sensordensity. FIG. 54 (5400) depicts a design which combines theinter-digitating fingers of the design in FIG. 51 (5100) and the flippedcolumns of the design in FIG. 53 (5300). FIG. 55 (5500) depicts theback-side of these two designs. FIG. 56 (5600) depicts a variation ofthe design in FIG. 50 (5000) where the area around each via is widenedinto to a diamond-shape. This design may reduce manufacturing cost andincrease sensor density by widening the conductor area around each via.It may also help make the sensor more accurate/linear with respect totouch position. FIG. 57 (5700) depicts the back-side of this design.

Force Sensing layer (FSL) Design

The force sensing layer (FSL) is composed of, or carries, the forcesensing material. There are a variety of possible designs for this layerfor both thru-mode and shunt-mode configurations. The main differencebetween these designs is the way in which they provide electricalisolation between adjacent sensor elements. With each of the designs,there are tradeoffs in terms of difficulty/cost of manufacture,difficulty of alignment/assembly with the other sensor layers, and levelof electrical isolation between adjacent elements.

One way to electrically isolate force sensing elements is to create asegmented force sensing layer (FIG. 46 (4600)). In this arrangement,there is a single patch of FSM that aligns to each sensing element. Thegap between the patches avoids electrical interconnection. This approachoffers the best isolation, but requires accurate alignment betweensensor layers. Another way to electrically isolate sensor elements is touse a patterned force sensing layer which has a fine pattern of FSMpatches (FIG. 48 (4800)). This pattern is at a smaller scale than theforce sensing elements themselves. Thus, multiple patches of FSM willcontribute to the sensitivity of each sensor element. This configurationremoves the need to have accurate alignment between the FSL and theforce sensing elements of the sensor. In this configuration, isolationis not perfect, as some of the FSM patches may form electricalconnections to neighboring sensor elements, but is good enough toprevent significant cross-talk between neighboring sensor elements.

Another similar configuration uses a pseudo-random pattern of FSMpatches (FIG. 49 (4900)) which have a smaller scale than the sensorelements. This pattern introduces some randomness into the patterned FSMapproach which may help to improve sensor consistency. There is anotherway to create an array of force sensing elements without needing topattern the force sensing layer. This approach employs a very thin layerof FSM. Because the layer is very thin, it has a high resistance in theplane of the material, compared to the resistance in the directionperpendicular to the layer. Thus, although the FSM allows current pathsbetween sensor elements, the resistance between them is so high that theeffect of this current is negligible. Because the FSM is not patterned,it does not need to be aligned to the other sensor layers.

Another method of isolating sensor elements is to coat the row and/orcolumn electrodes with force sensing material. FIG. 42 (4200) depictswhat this looks like when applied to a thru-mode sensor. Note that thisdesign does not need a layer in between row and column electrodes. Thecoating of force sensing material may be segmented, patterned, orpatterned with a pseudo-random pattern. Alternatively, a very thin layerof force sensing material, which has negligible in-plane resistance, canbe deposited over the entire pattern of conductors. For shunt-modesensors, a similar approach would be to coat the electrodes on the upperlayer of the PCB with FSM. In this case, the top layer can employ one ofthe FSM patterns described above, or it may just use a patternedconductive layer, since force sensitivity would be provided by thebottom layer.

Finally, it is possible to create a sensor where the electrodesthemselves have force-sensing characteristics. For instance, anelectrode patterned from carbon nanotubes may conduct very well, but mayhave a rough surface structure which results in an analog pressureresponse.

Interchangeability of Row and Columns

From an electrical perspective, either the row or column electrodes canbe used as the drive side, with the other side acting as the sense side.Similarly, from the perspective of sensor construction, row and columnelectrodes may be swapped. Thus, in thru-mode configurations, the rowscan be on the top layer and the columns can be on the bottom layer andsimilarly, in the shunt-mode configuration, the columns can be routedthrough the back-side and the rows can be patterned onto the front-sideof the circuit board. Although these choices may have some effect onsensor performance, they would typically be based on factors such asease of sensor layout, mechanical considerations, and electricalinteractions with external components. For example, it may beadvantageous to place the drive side closer and the sense side fartherfrom sources of electrical noise, such as a display.

Non-Rectangular Sensor Arrays (5800)-(6000)

With IFSA technology, non-rectangular arrays such as those depicted inFIG. 58 (5800)-FIG. 60 (6000) can be created. The array in FIG. 58(5800)-FIG. 60 (6000) is rounded, with a circular opening in the center.To create such a non-rectangular array, the present invention startswith a normal rectangular array as described earlier and removes sensorelements that fall outside of the desired final shape. At the same time,all the row and column electrodes must remain electrically connected;however, in areas where senor elements have been removed, the presentinvention can squeeze down the row and column electrodes to hug theoutline of the shape since there are no sensor element there. Anon-rectangular thru-mode sensor can be made in the same manner. Theresulting non-square sensor is scanned electrically in the same way asthe original square sensor, and it will also perform the same as asquare sensor, so there is no difference from the perspective of theelectronics and software. The only difference is that this new sensorjust will not be sensitive to touches in areas where sensor elementswere removed.

Interpolation Resistors

For the purposes of reducing manufacturing cost, the set of fixedinterpolation resistors between adjacent row and column electrodes wouldtypically be located on the same substrate as the sensing area. However,some embodiments could have the interpolation resistors located in aseparate location.

The resistances can be provided by any of a number of known ways ofcreating a resistor, including a resistor component, a printed carbonstrip, or another type of resistive material. The value of all theresistors is preferably well controlled and within a known target range.This is especially easy to do with discrete surface mount resistors,which come in a wide variety of sizes and are available with an accuracylevel of 1% or better. The resistance level of the row and columninterpolation resistors can be the same or different, and is chosendepending on the requirements of the drive and readout circuitry.Typically, higher value interpolating resistors reduce powerconsumption, but cause a loss in accuracy (because of the nonlinearitiesmentioned earlier), and vice versa.

When a carbon strip is used, it can simply be printed across theadjacent electrodes. As long as the spacing between the electrodes isfairly constant and the width and height of the strip is consistent, theresulting resistance value between electrodes will be consistent aswell. The resistance level can be controlled by varying the compositionof the resistive ink or the width/height of the printed strip. Theconsistency can be further improved by trimming the resistors after themanufacturing step with a method such as laser trimming.

In the illustrations, the interpolating resistors are placed in the areabetween the sensing area and the drive/sense electronics. In practice,interpolating resistors can be placed anywhere, as long as theyelectrically interconnect adjacent row electrodes and adjacent columnelectrodes. For example, they can be placed on the opposite side of thesensor, away from the drive/sense electronics. They can also be placedon the back-side of the PCB (using vias to make the connection),interspersed within the sensing area between the sensing elements, andeven embedded within the PCB itself. Finally they can be located in acombination of different locations on a single sensor. For example, someinterpolating resistors for the row electrodes may be to the left sideof the sensing area, while others may be on the right side.

Manufacturing Processes (6100)

The conductive layers for the sensors can be manufactured with a widevariety of manufacturing processes. All materials, including the FSM arechosen to withstand expected environmental and mechanical conditions fora given application such as repeated flexing, heat, and humidity.

Arguably, the most straight-forward is to use a standard rigid and/orflexible PCB manufacturing process to form the electrodes on asubstrate. The process typically starts with an FR4 (for rigid) orKAPTON® (for flex) base material which is coated with a layer ofcontiguous copper. The copper is then etched to create a pattern ofcopper conductors. Typically these need to be plated with an inertmaterial, such as gold, to avoid oxidation.

Alternative plating processes such as ENIG (Electroless Nickel ImmersionGold) or a layer of screen-printed carbon can be used to reduce the costof plating. In such circuits, standard surface-mounting (SMT) processescan be used to attach the interpolating resistors. For shunt-modesensors, vias can be formed using a standard process which involvesdrilling holes and then plating to form connections between two layers.Via filling can be used to fill the resulting holes and leave a smoothsurface.

Another approach is to use a printed electronics (PE) process whereconductive particles are deposited onto a substrate such as PET orPolyimide (KAPTON®) in an additive fashion. Some common conductivematerials used in these applications consist of carbon nanotubes, silvernanowires, and polymer inks that are filled with conductive particles.One commonly used material for printed electronics consists of a polymerink loaded with silver particles, which is typically deposited with ascreen printing process. Because materials such as this can degrade as aresult of mechanical stress, oxidation, or reaction with othergases/compounds, they may be passivated by over-coating with carbon or aforce sensing material. Furthermore, because it is difficult to solderto such a circuit, a printed carbon strip can be used to createinterpolation resistors. For thru-mode sensors created with a printedelectronics (PE) process, a very similar construction can be used aswith rigid/flexible PCB sensors. For the shunt-mode sensors, vias can becreated in a fashion similar to how vias are created on a PCB—bydrilling holes through the substrate with a drill or laser, followed byan overprint of a conductive material. An alternative is to print thebottom conductor layer, followed by printing an insulator layer withholes in the equivalent places where vias would be on a rigid/flex PCBsensor. Next, the top conductor layer is printed. The holes in theinsulator layer allow the pads in the top conductive layer to bridgeelectrically with the conductive traces on the bottom layer. Thiscreates the same electrical structure, but both conductor layers end upon the top side of the substrate separated by a thin layer of insulator(with holes in the locations of the vias).

Yet another method for making shunt-mode sensors is to print thetop-side of the sensor pattern first, which may be similar to any of thepatterns described earlier for making shunt-mode sensors. As before, thecolumns are connected within the pattern itself. However, the rows areconnected by small bridges. The bridges can be created by depositing asmall area of insulator material in each area where a column electrodelies in between two portions of a row electrode. Next, a smallconductive “bridge” is deposited over the insulator, connecting the twoadjacent portions of a row electrode. This sequence (6101, 6102, 6103)is generally depicted in FIG. 61 (6100).

Other approaches for forming electrodes can include vapor-deposition ofmetals or conductive materials such as carbon nanotubes. Patterning canbe done by a variety of methods including depositing through a stencil,offset press, laser etching, or transfer processes. IFSA sensors canalso be created using techniques for making cloth. Conductive threadcoated with FSM can be used to create the row and column electrodes. Rowelectrodes would run in one direction while column electrodes would runin the other direction, forming the warp and weft of a fabric. A forcesensing element would be formed at the intersection of each row andcolumn electrode simply as a result of two or more threads coated withFSM touching each other at right angles. At the edges of the cloth,resistive elements interconnect the row and column electrodes, and aconnection to the electronics is created using conductive material whichattaches at regular intervals to the edge of the force sensing array. Inthis design, the resistive elements would typically be made of a printedresistive rubber/paint, or a resistive thread that is tightly wound orknotted over the row threads and over the column threads to form anelectrical connection.

Transparency of Sensor Array

To create fully transparent sensors, transparent materials may be usedfor the force sensing materials, conductors, and various substratelayers of a sensor array.

Transparent force sensing materials have been described above.Transparent conductors can include materials such as indium tin oxide(ITO), carbon nanotubes, graphene, silver nanowires, fine-mesh copper,and organic conductors. Substrates can include glass, flexible glass,and polymers such as PET, Polyimide, or Polycarbonate.

Both shunt-mode and thru-mode configurations can be created that areidentical to their non-transparent counterparts, except that all theincluded materials are transparent. One notable configuration that wouldbe straightforward to produce with available manufacturing processes isthe shunt-mode diamond-shaped sensor pattern with bridges to connect thediamonds along the rows. See FIG. 61 (6100). To create the IFSA sensor,this pattern would be overlaid with a transparent force sensing materialon top.

Another option is to create a partially transparent sensor. This can bedone with much more standard materials and techniques. For example, witha shunt-mode sensor, light can shine through the vias, and openings canbe provided in the force sensing layer to let light through. A thru-modesensor can be manufactured with opaque electrodes on a transparentsubstrate, with gaps in the force sensing material that permit lighttransmission. Light would be able to shine through the gaps in theelectrodes and force sensing materials.

Assembly

Final assembly of IFSA sensors consists of laminating or holding thelayers together. Typically, pressure-sensitive adhesive would be appliedaround the perimeter(s) of the layers. The active area is typically leftwithout adhesive, as air or some other non-conductive fluid (such asmineral oil) is necessary in the active area for the force-sensingmaterial to operate. However, small adhesive areas may be providedwithin the active area of the sensor to keep the top layer fromde-laminating from the bottom. An air-gap/air-channel is typicallyprovided to allow air-pressure inside and outside the sensor toequalize. A filter may be added to the air-gap/air-channel to preventparticles or moisture from entering the active area. Sensors may behermetically sealed for operation in harsh environments. The top and/orbottom layer may be laminated to other layers such as a display,midframe, or other sensor. Sensor assembly should be done in a cleanenvironment, such as a cleanroom, to avoid particles or othercontamination from entering the sensor which can cause inconsistentperformance.

Curved or Flexible Sensors

The IFSA technology can be used to create curved or flexible sensors inseveral different ways. Flexible sensors can be created by usingflexible substrates such as Polyimide (also known as KAPTON®), PET, orPolycarbonate for the circuit, and using flexible materials for the FSMas well.

To create a sensor that is permanently curved, a flexible sensor can belaminated onto a curved rigid surface, or it is possible to start with aflat sensor and mold it into/onto a non-flat surface. It is alsopossible to directly manufacture the sensor electrodes on a curvedsurface using known techniques such as Laser Direct Structuring (LDS) orby 3D printing using both conductive and insulating materials. In thecase of shunt-mode sensors, the force sensing layer can be pre-moldedinto a curved shape and can be made out of a deformable material such asmolded silicone. In this case, force sensing material can be directlydeposited onto, or molded into, the force sensing layer. Alternatively,the entire force sensing layer can be made from a flexible/deformableFSM.

There are many applications in which it is desirable for the sensor toremain flexible. For instance, one may want to place sensors into aflexible phone/tablet, the wrist band of a watch or bracelet, into thesole of a shoe, or into clothing. In these cases, sensors built on aflexible substrate can be directly embedded into the application. Theymay also be manufactured in a fashion similar to how cloth ismanufactured, as described earlier.

The sensors can also be designed so that they can be bent/cut (withoutdamaging the traces) to allow them to wrap around or fold into complexshapes. For example, a robot fingertip can be covered in an IFSA sensorby making two cuts in the sensor pattern and joining the edges together(FIG. 62 (6200)). This shape can then be laminated or adhered to thesurface of the robot fingertip. The outside can be coated with a rubbershell to distribute force and provide a softer touch. In the case of ashunt-mode sensor, the inside of the rubber shell can be coated with FSMso that it can directly act as one part of the force sensing element, orthe entire rubber shell can be impregnated with conductive particles sothat it behaves like an FSM.

Electronics Details

The electronics for scanning an IFSA consist of several components.These components are meant to illustrate one embodiment of theinvention. It should be clear to the reader that alternative variationsand combinations of components can be used in keeping with the spirit ofthe disclosure. Furthermore, some components may be integrated together(for example, via an integrated circuit or ASIC), can be implemented insoftware, or removed altogether without substantially limiting theability to scan the sensor.

Voltage Source

The purpose of the voltage source is to provide a constant voltage fordriving the IFSA sensor. Active electronics, such as an amplifier or alinear/switching voltage regulator may be used to provide the constantvoltage. The voltage source may be a separate source from the voltagesource used to drive the digital portion of the circuitry, or it may beone and the same. There may also be some current-limiting capabilitybuilt into the voltage source to avoid excessive current draw by thesensor. The current-limiting capability can be implemented simply with afixed resistor, can be a soft limit designed into the voltage sourcecircuitry, or can be implemented as a hard-cutoff when a certain currentlevel is reached. The current-limiting capability can also beimplemented using the digital circuitry. When the microcontrollerdetects an over-current condition, it can decide to shut off scanning,or modify the state of the scanning hardware to reduce powerconsumption.

An analog line may be provided that can be used to monitor the voltagegenerated by the voltage source. This can be used to detect and/orcompensate for drops in voltage due to excessive current draw. Thecompensation can be done via analog circuitry. One way to do this is tofeed this voltage into the voltage reference of the ADC used to scan thesensor. Alternatively, this compensation can be done digitally bymeasuring the voltage generated by the voltage source using an ADC andthen multiplying the values read from the sensor by the expected drivevoltage divided by the measured voltage.

Drive Circuit

The job of the drive circuit is to drive each active column electrodeeither to ground or to the voltage level provided by the voltage source.It accomplishes this with a series of analog/digital switches connectedto each active column electrode. The column switches may also beprovided with the ability to disconnect one or more columns (puttingthem into a high-impedance state). This can be used for multi-resolutionscanning. The control of the column switches within the drive circuit isperformed by the control logic, although some aspects of the controlsequences may be automated/pre-programmed. Typically, during operation,only one column at a time is driven to the voltage provided by thevoltage source, while all the other columns are driven to ground ordisconnected (in a high-impedance state). In one embodiment, the drivecircuit uses analog switches to connect the column that is being drivenhigh to the voltage source. In another embodiment, the drive circuitcould use digital switches to perform the same function. In yet anotherconfiguration, the drive circuit could include an integrated voltagesource. The integrated voltage source can be shared among all the columnelectrodes, or there may be multiple voltage sources (as many as one foreach column).

Sense Circuit

The sense circuit is similar to the drive circuit, but instead ofdriving rows to a particular voltage, it either connects the row to bemeasured to external circuitry or connects the row to ground. Like thecolumn switches, the row switches may also be provided with the abilityto disconnect one or more rows (putting them into a high-impedancestate), which can be used for multi-resolution scanning. The control ofthe row switches within the sense circuit is performed by the controllogic, although some aspects of the control sequences may beautomated/pre-programmed. During operation, typically only one row at atime will be connected to external circuitry. However, in order to allowfor faster scans, some embodiments may have multiple copies of thesignal conditioning circuitry and/or ADCs. In this case, the sensecircuit could also allow multiple rows to be connected to externalcircuitry at the same time. All other rows would typically be connectedeither to ground or disconnected (in a high-impedance state).

The sense circuitry may have additional features to support low-powerwakeup from a touch (as described in the next section). Also, becausethe drive and sense circuitry is so similar in function, it may beimplemented using a common design. In other words the same chip, ASIC,or circuit could be used as both the drive circuit and sense circuit.The drive and/or sense circuitry can also be designed as a module thatcan support some fixed number of active row/column electrodes. Largernumbers of row/column electrodes could be supported in a givenembodiment simply by increasing the number of these modules.

Signal Conditioning Circuitry

The signal conditioning circuitry takes the raw signal from the sensecircuit and prepares it for being read by an ADC. To increase thelinearity of the signal produced by the sensor, it is desirable to drivethe row being read to ground potential. Thus, the most linear signalconditioning circuit will include a transimpedance amplifier which willdrive the input to ground potential, while measuring the amount ofcurrent necessary to do so, and feeding that value to an external ADC. Aless accurate but simpler method of measuring the current is simply touse a low resistance value pull-down resistor connected to ground, andmeasuring the voltage across the resistor. In cases where this voltageis too low to be read by an ADC, this voltage can be amplified to matchthe output range to the range of the ADC and reduce noise. Because thesensor itself already has a resistive path to ground (through theinterpolation resistors), even the resistor to ground may be left out,but the resulting output signal will be even less linear.

The signal conditioning circuit can also include filtering to reducehigh-frequency noise. This can be in the form of a passive filter (suchas an RC low-pass filter), an active filter (such as an op-amp low-passfilter), or simply a capacitor to ground (since the sensor itself canprovide the R portion of the RC filter).

An amplifier can also be used to take the relatively high-impedancesignal from the sensor and turn it into a low impedance signal for theADC, or to boost low voltages from the sensor. A programmable gainamplifier can be used to dynamically adjust the sensitivity of the sensecircuitry, and a resistive divider can be used to reduce the voltage ifit is too high for an ADC.

All of these different approaches are known ways of pre-conditioning asignal before feeding it into an ADC. The particular choice andarrangement of these elements depends on the sensor accuracy requiredand a tradeoff between accuracy, complexity, power consumption, circuitsize, and price. The signal conditioning component can be omitted, butthis may result in reduced sensor performance. Note that the signalconditioning circuit can be an independent circuit, or can beincorporated into the sense circuit, into the ADC, or parts of it may bebroken up among different components.

ADC

The ADC (analog to digital converter) takes a voltage level produced bythe signal conditioning circuit and converts it into a digitalrepresentation suitable for processing by a microcontroller. Typically,a successive approximation register (SAR) ADC with at least 8 bits ofresolution is used. Greater ADC resolution results in more accurateposition and force measurements. The conversion speed of the ADC is alsoimportant as it is typically the limiting factor for how fast a sensorcan be scanned. As described earlier, multiple ADCs (along with multipleconditioning circuits) can be used in parallel to increase scanningspeed. Another factor which affects sensor scan rate is the settlingtime for the sensor, drive/sense circuitry, and conditioning circuit.Enough time must be given after switching the state of the drive orsense circuitry for the analog input voltage to the ADC to settle.Furthermore, the ADC itself may carry residual charge from the previousmeasured voltage. Sufficient acquisition time must be given for the ADCto sample the input voltage, especially if the input impedance to theADC is high. Alternatively, the ADC sampling capacitor may be reset to aconsistent state after each sample to avoid any residual charge from theprevious sample.

Digital filtering techniques may be used to improve thesignal-to-noise-ratio (SNR) of the signal read by the ADC. For example,multiple ADC readings can be combined with a technique such asaveraging, or filtered in ways such as a median filter to reduce noise.A transformation into the frequency domain can be used to detect desiredfrequencies or suppress unwanted frequencies.

Also, the digital voltage output from the ADC can be remapped into adifferent value using a lookup table or a mathematical calculation toconvert the signal into a more useful range, or compensate fornon-linearity in the electrical system.

Controller

The controller is the component which performs scan sequences, collectsdigital values from the ADC, optionally processes those values, andoptionally sends information to an external system via an IO interfacesuch as I2C, SPI, UART, USB, Bluetooth, Wi-Fi, etc. Parts of thescanning circuitry including the voltage source, drive circuitry, scancircuitry, signal conditioning, and/or ADC can be incorporated into thecontroller. The controller may have a program memory which allows codeto be loaded with different control sequences/algorithms to change thebehavior of the system. Additionally, the controller can usefixed-function logic to automate/accelerate common operations such asscanning or processing the values read from the sensor.

Scanning Details

In addition to the basic full resolution scan of the sensor describedearlier, there are several other ways to scan an IFSA sensor that allowdifferent tradeoffs between scan speed, resolution, precision, power,and area. Some of these other approaches can also be used to implement alow power wakeup mode, where the sensor can be in a very low powerstate, but can still detect the presence of a touch, which can be usedto wake the system or trigger a transition into a fast/high resolutionscanning state. This section describes some different ways in which anIFSA sensor can be scanned and mentions some of the tradeoffs associatedwith these approaches.

Basic Scan

The most common way to scan the sensor is the method described earlier.It consists of driving one column at a time, and for each column that isdriven high, sensing the value on each row one at a time. Thisprogressively scans the intersection of every active row and everyactive column electrode. When scanning a sensor element at a particularrow/column intersection, all other active column and row electrodes aregrounded, creating an interpolation area around that column and rowelectrode that is two times larger than the distance between adjacentactive columns and adjacent rows (FIG. 34 (3400)). The time required forthe basic scan is proportional to the number of active row electrodestimes the number of active column electrodes.

Parallel Scan

The parallel scan is a variant of the basic scan which improves scanspeed without sacrificing resolution. Scan speed is improved byperforming ADC conversion on more than one row simultaneously. To dothis, there needs to be more than one instance of the signalconditioning and ADC circuitry operating in parallel on multiple rows.

To preserve the interpolation property, there must be at least onegrounded active electrode in between each pair of sensed electrodes.However, in embodiments where the sense electronics grounds the sensedelectrode (as described earlier, this can be accomplished by pulling theelectrode low with a transimpedance amplifier, or using a pull-downresistor with a low resistance value), each electrode is effectivelygrounded when it is being scanned. This allows, in the limit, scanningall rows simultaneously.

The advantage of the parallel scan is that it can greatly increase scanspeed and reduce power consumption, since the scan can happen in ashorter timeframe, allowing the sensor to be powered for a shorter time.The downside is that more electronics may be required to support this.The time required for a parallel scan is proportional to the number ofactive row electrodes times the number of active column electrodesdivided by the number of rows that can be sensed in parallel.

Scan Rate

The rate at which the sensor is scanned can be dynamically decreased toreduce power consumption or increased to reduce input latency. Onestrategy to reduce power consumption is to perform scans at a low rate,for example, 10 frames per second until a touch is detected, and then toincrease scan rate to a higher rate, for example 60 frames per secondafter a touch is detected, and continue scanning at the higher rateuntil all touches are removed.

Reduced-Resolution Scan

Another strategy that can be used to reduce power or increase scan speedis to dynamically reduce the resolution of active rows and/or activecolumn electrodes by putting some active electrodes into a highimpedance state, effectively disconnecting them electrically from thedrive and sense circuitry. This does not significantly reduce theresolution with which a contact can be sensed, because the disconnectedelectrodes effectively act as additional interpolating electrodes, butreduces the distance at which multiple touches can be distinguished.

For example, resolution along the X and Y axes can be cut in half byputting every other active row and active column electrode into a highimpedance state. Resolution can be reduced further by putting largernumbers of row and column electrodes into a high impedance state. Forexample, to reduce the X and Y resolution by one quarter, one would keepevery fourth active electrode electrically connected and each set ofthree active electrodes between each of these would be put into a highimpedance state. As the resolution is decreased, the number ofrow/column junctions that must be scanned decreases as well. Thisreduces power consumption and increases scan speed. In some cases, itmay be desirable to set different row and column resolutions, or even tohave different row and/or column resolutions in different areas of thesensor. Taking this approach to the limit, the result ends up with thelowest resolution scan, where all the columns except the first and lastcolumn and all the rows except the first and last row are put into ahigh impedance state. During the scan, the present invention would drivethe first column followed by the last column, while sensing on the firstrow and the last row for each powered column. In total, only four ADCvalues would be collected. Using these values, the present inventionwould be able to compute the average X and Y position of all touches andthe total force of all the touches.

Although the present invention gives up multi-touch sensing capabilityby doing this kind of scan, the present invention gains the ability toscan incredibly fast, with very little power consumption, which can beuseful in situations where very fast events are to be detected or wherepower is being conserved such as in a battery powered device.

Multi-Resolution Scan

Because scan resolution can be varied dynamically, it is possible tocombine scans of multiple resolutions in interesting ways. For example,it is possible to overlap multiple low resolution scans (offset bydifferent amounts in X and Y) to create a higher resolution final forceimage. Low resolution scans can also be used to enable a wake-up mode,where the sensor is scanned at a lower resolution until a touch isdetected and then the resolution can be boosted to accurately determinethe position of the touch. It is also possible to perform a lowresolution scan, and then refine it by performing higher resolutionscans in areas where touches are detected. This methodology has theadvantage of combining the power efficiency and high speed of lowresolution scanning with the precision of a full resolution scan.

Window-Area Scan

When the location of a touch is known in advance, or only touches in aportion of the sensor area are of interest, it is possible to perform ascan in a small window rather than scanning the entire sensor, simply byiterating only through the rows and columns of interest. The window canbe moved and/or sized dynamically to follow a touch, and there can evenbe multiple windows that are scanned at the same time over different,possibly overlapping locations on the sensor.

One and Zero Dimensional Scan

All of the scan approaches described previously scan a grid of sensorrow/column junctions. However, when it is only necessary to detectwhether or not a touch has occurred irrespective of the position, or itis necessary to track a contact in only one dimension, it is possible toperform an even faster scan. One way to accomplish this is to power onall the columns and then sense on one row at a time. This would provideonly the Y position of a touch, but would reduce the number of readingsthat need to be taken to the number of active rows in the sensor. Thiscan also be combined with the reduced resolution scan idea presentedearlier to reduce the number of active rows that need to be sensed, atthe expense of reducing Y resolution.

An alternate way to do this is to ground all the rows and power on onecolumn at a time. Touches on or near the powered active column electrodewill cause increased current flow from the voltage source. One way tomeasure this increased current flow is by placing a small value resistorin line between the voltage source and the drive electronics and takinga differential voltage measurement of the voltage across that resistor.

Alternately, in cases where the voltage source voltage drops as itsupplies increased current, the present invention can measure the dropin the voltage output by the voltage source. Doing this would provideonly the X position of touch, and would reduce the number of readingsthat need to be taken to the number of active columns in the sensor.This can also be combined with the reduced resolution scan ideapresented earlier to reduce the number of active columns that need to besensed, at the expense of reducing X resolution.

Furthermore, it is possible to make the entire sensor act as one giantpressure-sensitive button. One way that this can be done is by modifyingthe sense electronics to allow all the rows to electrically connect to asingle analog input. By powering all the columns and sensing on all therows simultaneously, the entire sensor becomes one largepressure-sensitive button. Alternatively, the present invention canpower all the columns and ground all the rows, and simply measure theincreased flow of current to the column electrodes, or a voltage drop inthe voltage of the powered columns. Yet another way to do this is toelectrically connect to the force sensing material (this works best indesigns where the force sensing material is contiguous). This then formsone electrode, while all the rows and columns form the second electrode.In this case, the present invention can ground all the row and columnelectrodes, power the FSM, and measure current flow through theconnection to the FSM, or the amount of the voltage drop on theelectrical connection to the FSM.

Many other variations of these three schemes are possible. For example,with all of these approaches, the present invention can flip thepolarity (power what is grounded and ground what is powered), and stillachieve the same result. It is also possible to measure currentflow/voltage change on either side of any of these circuits and insteadof measuring the current flow/voltage change on the powered line, thepresent invention can measure it on the grounded line or vice versa.

In general, all of these approaches turn the sensor into either a linearposition sensor or a single pressure-sensitive button, which greatlyreduces scan time, and increases scan speed while sacrificing theability to acquire a two-dimensional force image. These approaches,especially the ones which turn the entire sensor into a singlepressure-sensitive button, can be useful when a low power wakeup isdesired. For example, on a battery powered device, the present inventionmay want the device to go into a low power state whenever the device hasnot been touched for some time. In this state, the present invention canconfigure the circuit so that the present invention can read the valueof a single electrical line or a small number of electrical lines todetermine whether a touch has occurred anywhere on the sensor.Furthermore, this signal can be fed into a hardware wakeup/compare linesuch that the wakeup can occur without the intervention of any software,allowing the processing unit to be fully shut down when the sensor hasnot been used for some time, and to wake back up immediately when atouch occurs.

Processing Details

In applications that require touch tracking, after acquiring a forceimage, the controller typically processes that image to detect and trackcontacts, which are localized areas of force on the sensor. Thefollowing set of steps can be performed to detect and track contacts.

Normalization

Either before or after the baseline subtraction step (described later),it may be desirable to re-scale the input values into a known scale. Forinstance, it may be desirable to take the raw ADC values from the sensorand map them to known forces such as grams. This can be done via lookuptables, or using mathematical equations. A calibration step may be usedat the time of manufacture or when requested to recalibrate the mapping.The calibration may be global (applying to the whole sensor) or can bedone at various locations on the sensor. In the latter case, thecalibration values can be smoothly interpolated over the whole sensor,with the assumption that variation is gradual over the surface of thesensor.

Baseline Subtraction

The purpose of the baseline subtraction step is to eliminate areas ofnon-zero pressure which may be caused by imperfections in the sensor,imperfections in device assembly, or persistent pressure points, such asif an object were resting on the sensor. The baseline subtractionalgorithm processes one pixel of data in the force image at a time. Foreach of these pixels, it stores a baseline value, which is subtractedfrom the force image at each frame. Typically, the baseline is set fromthe values read out from the first scan of the sensor after it is turnedon. The baseline can then be updated from time to time based on thecurrent baseline value and the current force sensor reading at aparticular sensor location. Typically, the baseline is updated to avalue somewhere between the current baseline value and the value of thecurrent sensor reading. If the amount of increase/decrease in thebaseline value per frame is fixed, the baseline will change at aconstant rate over time. Alternatively, the rate of increase/decreaseper frame can be set as a percentage of the difference between thecurrent pressure reading and the current baseline value. In this case,the baseline will change faster if the difference is greater, and slowerwhen the difference is small. The rate of change can be set to controlthe rate at which changes in the force distribution are eliminated.

In some applications, the present invention may want the rate of changein the baseline value at each sensor element to be different, dependingon whether the baseline is increasing or decreasing. This is because itis often desirable for the baseline to increase slower and decreasefaster so that if a user holds down on the sensor for a while, thebaseline will increase slowly, avoiding the possibility of throwing offfuture measurements. Furthermore, if the baseline decreases faster thanit increases, the baseline will be able to return to normal more quicklyonce the user releases the touch on the sensor.

Blob Detection

Typically, the next step after baseline subtraction in processing apressure distribution is blob detection. Blob detection uses analgorithm that processes the force distribution row by row or column bycolumn to find connected areas of pressure points that have non-zeropressure and assigns to them a unique identifier. For each blob,statistics such as the (X,Y) position of the centroid, area, totalforce, pressure, and shape of matching ellipse are calculated.

Peak Separation

Peak separation is an optional step that can be used to furthersubdivide blobs that have more than one pressure peak. Peak separationstarts by finding the peaks within each blob. Next, a breadth-firstsearch or algorithm such as a watershed algorithm for the pixels aroundeach peak is performed, where only steps towards pixels with lower forcevalues, and which are not part of other blobs, are taken. Thiseffectively separates the area around each peak and also allowsneighboring peaks to be found. Statistics similar as those defined forblobs can be computed for peaks.

Algorithms may be used to adaptively split or merge peaks as desired.For example, it is often desirable to split the peaks formed by twofingers close together, so that the fingers can be trackedindependently. At the same time, it is usually desirable to merge thepeaks formed by the different bumps in a user's palm, to allow theentire palm to be tracked as one object.

Depending on the application and situation, the present invention maychoose to perform blob detection, peak separation, or both algorithmstogether to detect touches. In some cases where the present invention isnot interested in tracking touches, the present invention may do neitherof these steps and simply report the array of force readings read fromthe sensor to the user.

Position Compensation

Because there may be some inherent non-linearity in the sensor, once thepresent invention has coordinates for blobs, peaks, or contacts, it maybe desirable to apply a compensation for the non-linearity to increasetracking accuracy. The compensation is essentially a series of (X,Y)position offsets which vary depending on the location on the sensor.

These offsets can be experimentally measured or mathematicallypre-computed at the time the sensor is designed or manufactured, andstored into the sensor's memory. The compensation will take an input(X,Y) position and remap it to a nearby output (X,Y) position. Thecompensation may also take other factors such as the force or area ofthe contact into account to make a more accurate adjustment. It may alsobe applied for some contacts, but not others. For instance, if the useris writing with a stylus on the sensor, the present invention may wantto apply the compensation to achieve the highest possible accuracy.However, the present invention may choose not to apply the compensationif the user is touching the sensor with their palm, as the presentinvention may not care about the accuracy of the palm position sincethis type of touch is relatively large and imprecise.

Contact Tracking

In order to allow software to make sense of the touches over time, it isnecessary to track touches between consecutive frames. In the contacttracking step, the present invention iteratively matches contacts fromthe new frame to contacts in the old frame. Typically the (X,Y) distancebetween contact centroids is the key metric used to perform thematching. Each time a pair of contacts is matched, the contact in thenew frame is given the ID of the contact in the old frame, and a“contact moved” event is generated. Any contacts that are detected inthe new frame (that were not in the old frame) are treated as a newcontact and given a new ID, generating a “contact start” event. Anycontacts that were in the old frame but are not found in the new framegenerate a “contact end” event, and the ID is subsequently recycled.

The results of the touch tracking algorithm may be fed back into thepeak separation algorithm. By doing this, the present invention canavoid touches from spuriously appearing/disappearing where there arenone as a result of the appearance of false peaks due to noise,variation in the sensor, and/or non-smoothness in the force distributionof a touch. This information can also help the peak separation algorithmdetermine which peaks should be split or merged. For example, in thepeak separation algorithm, if the present invention had detected a touchin the previous frame, the present invention may bias the peakseparation algorithm to try to find a peak corresponding to that touchin the next frame, and if there was not a touch in a particular locationin a previous frame, the present invention may bias the peak detectionnot to find a peak in that location in the next frame, or to merge itinto another peak. However, this feedback step must be implementedcarefully to avoid the situation where a touch that has gone awaycontinues to be tracked, or the situation where a new touch is notdetected because it was not seen previously.

Communication with External Components

Typically, external hardware and/or software components are interestedin receiving either force images, contact events, or both. Thecommunication interface handles configuration of the sensor, and sendingof force images and/or contact events. Typically, communication startswith a hand-shake which gives the external components information aboutthe sensor such as its version, size, range of forces sensed,capabilities, etc., and establishes the operating parameters of thesensor. The external components then establish what information theywould like to request. Next, a data stream is established which sends astream of information from the sensor at a predetermined frame rate oron the occurrence of a predetermined event. This configuration continuesuntil the external hardware and/or software requests a termination ofthe data stream or a change in characteristics of the stream such asframe rate, resolution, what data is being sent, etc., or the connectionis broken.

Other Embodiments

Active Interpolation Electronics

Instead of using resistors to create the interpolation property alongrows and/or columns, it is possible to use active electronics(consisting of transistors, op-amps, etc.), to create the linear falloffof voltages on the drive side and the linear split of current on thesense side. The benefit of active electronics is the ability to reduceor eliminate the non-linear interpolation behavior described earlier,which results from a change of potential on the drive and senseelectrodes as a result of current flow through sensor elements. Theactive electronics may be instantiated on a per column/row basis, orspecialized circuits can be created that perform interpolation over aseries of rows or columns. For example, an IC could be designed thatwould connect to each pair of adjacent active electrodes, and also toeach of the interpolation resistors between that pair of activeelectrodes, and create the interpolation property (either voltagefalloff or current splitting) over that set of electrodes.

Active electronics for creating the interpolation property on the driveside can be made with a resistive voltage divider circuit (similar tothe interpolation resistors) and a series of operational amplifierswhich are configured as voltage followers to generate that same voltageat their output. The outputs of the operational amplifiers are connectedto the drive electrodes (both active and interpolating). The resistivedivider circuit will in this way be electrically isolated from theoutput of the sensor array, eliminating nonlinearity due to current flowthrough the sensor elements.

Active electronics for creating the interpolation property on the senseside can be made with a series of transimpedance amplifiers connected tothe sense electrodes (both active and interpolating). Eachtransimpedance amplifier will try to keep the sense electrode that it isconnected to at a ground potential. On its output, it will produce avoltage proportional to the current flowing through the sense electrode.The output voltages of the transimpedance amplifiers connected to thesense electrodes can be averaged using an averaging circuit, where thecontributions of the different electrodes are weighed differently tocreate a linear falloff in sensitivity. Another way to implement thesense side is to use a transimpedance amplifier which feeds into atransconductance amplifier at each sense electrode. The output of thetransconductance amplifier can then be fed into a series ofinterpolation resistors similar to those found on a regular IFSA sensor.This combination, which can be described as a current mirror, willproduce a current at the output of the two amplifiers that isproportional to the current flowing through the connected senseelectrode, but the sense electrode will remain at a ground potential,thereby eliminating the non-linearity.

Partially Interpolating Force Sensor Arrays

While the embodiments described so far enable interpolation between eachpair of row and column electrodes, there may be applications where it ispreferable to mix sensor regions with interpolation and other sensorregions without interpolation, or to have interpolation along one sensoraxis but not the other.

In one embodiment, it is possible to have interpolating resistors onlyon the rows or only on the columns. This would create interpolationalong one axis, but not along the other, for applications where theheightened sensing accuracy or reduced quantity of drive/senseelectronics provided by interpolation is only needed on one axis.

In another embodiment, it is possible to leave out the interpolationresistors between some pairs of adjacent columns or some pairs ofadjacent rows. This would have the effect of breaking up the regions inwhich interpolation occurs, creating separate interpolating sensor zonesin proximity of each other. In this design, the electrodes on eitherside of the “break” in interpolation resistors would preferably beactive electrodes so that each separate interpolation zone could bescanned all the way to its edge.

Non-interpolating Force Sensing Arrays

With all of the described shunt-mode and thru-mode sensorsconstructions, it is also possible to enable non-interpolating scanning.In this case, there would not be any interpolation resistors. Instead,the multiplexing circuitry would allow the drive and sense electronicsto connect any of the electrodes. In other words, all the electrodes arenon-interpolating. The multiplexing electronics could also allowconnection to multiple electrodes at the same time (for lower resolutionand multi-resolution scan modes).

With this approach, it may be possible to more accurately measureposition of a contact, to perform better disambiguation of multipletouches, and to better calculate the touch area. For applications thatinvolve a stylus and a finger, it may be possible to distinguish astylus from a finger touching the sensor simply by measuring the area ofthe touch.

Furthermore, the multiplexing electronics could be designed in such away that they could switch between an interpolating mode and anon-interpolating mode. In the interpolating mode, only a subset of theelectrodes would be connected to the drive/sense electronics, and therest of the electrodes would be connected via interpolating resistors asin a normal IFSA. In the non-interpolating mode, all the electrodeswould be connected to the drive/sense electronics. This would enable anapplication to make use of the power, performance, and speed benefits ofinterpolating sensors, and the increased resolution of non-interpolatingsensors.

Integration of IFSA with Other Components (6300)-(6400)

Flexible Overlays and Underlays

The interpolation property of IFSA sensors allows the ability toincrease the resolution of the sensor relative to the drive electronics.For tracking objects, such as fingers, that would typically be muchlarger than the distance between sensing elements/electrodes, thisapproach yields very accurate tracking. However, for objects such as astylus, the size of the contact area may be much smaller than thedistance between sensing electrodes. In this case, as the stylus movesover an IFSA sensor, there may be regions (near the centers of sensorelements) where the stylus tracking becomes discontinuous.

To improve the tracking performance for such objects, the presentinvention can add a thin flexible/compressible layer over the sensor.This layer will allow the object to slightly compress into the layer,increasing the surface area of contact, and thereby creating a morecontinuous tracking response. To clarify this further, assume thepresent invention is attempting to use a stylus which has a tip with a1.25 mm diameter, and the sensor the present invention is using hasapproximately a 1 mm distance (0.25 mm-2.5 mm) between nearby sensorelements. If contact is made with the sensor directly with the stylus,only a point contact will be made, and the sensor will be able to tellonly which sensor element is being touched, but not where the stylus isbetween sensor elements. Now, if the present invention adds a flexiblematerial which is 0.625 mm in thickness on top of the sensor, and touchit with the stylus, the stylus will be able to compress slightly intothe flexible material. As it compresses into the material, the surfacearea of the contact will increase to a diameter of approximately 1.25mm. Now, as the stylus moves across the surface, it will always activatemore than one sensor element. As a result, the present invention will beable to track it at a resolution significantly higher than the 1 mmpitch between sensor elements.

The only downside of this approach is that the flexible layer may bedifficult to write on, due to increased friction. To combat this, thepresent invention can put another thin textured layer on top of theflexible layer to improve the surface feel. In another embodiment, thepresent invention could add the flexible layer below the sensor as well,and achieve the same effect of increasing the contact area of thestylus.

Integration with Displays

IFSA sensors can be integrated with displays in order to create a touchdisplay. Transparent versions of the sensors can be overlaid on top of adisplay. Opaque versions of the sensor can be placed below a display.The possible display types include OLED, electrophoretic displays (suchas e-paper displays), LCD, and reflective LCD. In all of thesecombinations, care must be taken to avoid bumps or particles beingtrapped between the layers, as these particles can create pressureconcentrations that degrade sensor accuracy.

Today, most displays are built on top of rigid substrates such as glass.However, a rigid display may not transmit forces well enough to allowaccurate touch. Thus, it is preferable to use a flexible display.Advantageously, these display technologies can also be manufactured onflexible substrates, such as flexible polymer film or flexible glass,creating flexible displays. These flexible displays, when overlaid on anIFSA sensor, minimally affect IFSA sensor performance.

It may also be possible to integrate the IFSA sensing technology intothe layers of the display itself. For instance, it may be possible tocollocate the electrodes of the IFSA with the electrodes of a display,such as an LCD display, and to collocate the FSM with some of the otherlayers of the display, such as the color-filter/polarizer. As anotherexample, it is possible to place a transparent IFSA sensor in betweenthe TFT panel of an LCD and a backlighting illumination source.

In the case where it is desirable to have a display directly on top of ashunt-mode IFSA sensor, it is possible to have the display act as thetop layer. To do this, the bottom side of the display can be directlycoated with any of the already mentioned FSM materials such as printedcarbon ink. Alternatively, an FSM material such as a carbon-impregnatedfilm can be laminated, bonded, or fused onto the back side of thedisplay. Also, it is possible to create a display substrate whichalready has FSM impregnated into the bottom layer, so that there doesnot need to be an additional printing/lamination step onto the bottom ofthe display. In all these cases, the display would act as the top layerof an IFSA and it would simply have to be placed on top of a layer withthe shunt mode electrode pattern to create a combination display+IFSAsensor. Alternately, the bottom of the display substrate can act as thetop layer of a thru-mode sensor or the bottom layer (containingelectrodes) of a shunt-mode sensor. The benefit of all these options isthe possibility of increased yield, reduced cost, and reduced overallthickness.

Various layers in the display stack can also be designed to be flexiblein order to improve the resolution of stylus tracking as described inthe previous section. For example, in the case where a display has afront-light or a backlight, it may be possible to choose alight-transfer material that is flexible and transparent such assilicone. In this case, the front-light/back-light would help to createa better force distribution over the sensor, increasing trackingaccuracy. Additionally, this approach may help to improve display andsensor reliability by softening accidental impacts.

Integration with Other Sensing Technologies

IFSA sensors can be integrated with many other types of sensingtechnologies, including capacitive, electromagnetic resonance (EMR),optical, acoustic, etc. Some possible sensor and display combinationsare depicted in FIG. 63 (6300)-FIG. 64 (6400). Detailed below are someways in which IFSA can be integrated with these sensing technologies.

Capacitive Touch

A capacitive touch sensor can be overlaid on top of an IFSA sensor. Therows and/or columns of the IFSA sensor can even serve double-duty asrow/column lines on the capacitive sensor. This configuration can beused to increase the sensitivity of the system to very light touch. Thecapacitive sensor can also be used to detect finger “hover”/“proximity”above the IFSA sensor (it could also be used to detect proximity ofpalms, hands, faces, or other body parts/conductive objects to thesensor). Another benefit of this configuration is that it would bepossible to distinguish conductive objects, such as fingers, fromnon-conductive objects, such as a plastic stylus.

This is because the conductive object would have both a force signature(via the IFSA sensor) and a capacitive signature (via the capacitivesensor), while the non-conductive object would have only a forcesignature, and would be invisible to the capacitive sensor. Furthermore,it may be possible to use the combined signal of a capacitive sensor andIFSA to improve overall sensing accuracy and/or performance.

Because IFSA sensors can handle precise touch-tracking, the complexityand cost of the capacitive sensor can be reduced, and the capacitivesensor can be tuned for hover/proximity detection rather than touchdetection to enable both hover (via the capacitive touch sensor) andtouch and force sensing (via the IFSA force sensor).

Because the capacitive sensor may sense a touch before it is sensed bythe IFSA sensor, the capacitive sensor can also be used as a wakeupsource. This would allow the system to save power by shutting off theIFSA sensor whenever the capacitive sensor is enabled. Conversely, theIFSA sensor could be used to calibrate the capacitive sensor. Whenever a“contact start” or “contact end” event is registered on the IFSA, thecapacitive sensor can use these events to calibrate its touchsensitivity. In this way, the capacitive sensor's ability to measurehover distance/proximity can be dynamically refined at runtime.

Both mutual-capacitive and self-capacitive style capacitive sensors canbe used. Mutual-capacitive sensors consist of a set of row and columnelectrodes, forming a capacitor at the intersection of each column androw. Each of these capacitors can be measured by capacitive sensingelectronics to create a grid of capacitance values. The presence of afinger creates a capacitive coupling to ground which causes the measuredcapacitance between the row and column electrodes to drop.Self-capacitive sensors consist of one or more capacitive “pads.” Eachone has a connection to the sensing electronics. In a self-capacitivesensor, the capacitance of each pad to ground is measured. Thiscapacitance increases as a finger approaches. Mutual-capacitive sensorsare typically more accurate, but operate at a shorter range and are moresusceptible to electrical noise. Self-capacitive sensors are typicallyless accurate (since it is difficult to create a high-resolution grid),but can operate at a larger range, and are typically less susceptible toelectrical noise. Either one can be used with IFSA.

Because capacitive touch sensors can be made on a similar substrate asIFSA sensors, it may be possible to pattern all or some of a capacitivetouch sensor's layers onto the unused sides of an IFSA sensor. Forinstance, in a thru-mode IFSA sensor, it may be possible to pattern aset of cap touch sense electrodes onto the top side of the top substrateand to use the electrodes on the bottom side of the top substrate asboth the IFSA and cap touch drive electrodes. In a shunt-mode IFSAsensor, it may be possible to pattern a set of cap touch electrodes orareas onto the top of the force sensing layer.

In one configuration, the FSM of an IFSA sensor itself can be used as acapacitive touch sensor. In this configuration, one or more connectionswould be made to the FSM, and the sensor could alternately switchbetween a capacitive sensing mode and a force sensing mode. This wouldeffectively turn the FSM into a self-capacitive sensor, which would begood for detecting hover/proximity. In the capacitive sensing mode, theIFSA electrodes can be grounded/floating, allowing the capacitance ofthe FSM to be measured without influence from the IFSA row/columnelectrodes. In the force sensing mode, the FSM can be disconnected (orput into a high impedance state), and the IFSA can be scanned as usual.

In another configuration, the electrodes of the IFSA could be used tocreate a mutual capacitive sensor. In this case, the same sensor couldbe used for both capacitive and resistive sensing. This approach wouldenable light touch and hover/proximity sensing via the capacitive scanmode, and more accurate, higher pressure force sensing via the resistiveIFSA scan mode. The main challenge in this configuration is that the FSMcould block some of the electric field. To avoid this, the FSM could bedesigned to be transparent to some portion of the capacitive field ofthe sensor. Alternatively, in a shunt-mode IFSA, the entire sensor couldbe flipped upside down, so that the side with the electrodes becomes theside closer to the user, thus avoiding the problem altogether.

Another difficulty with using the electrodes for both capacitive andresistive sensing is that the interpolating resistors could interferewith capacitive measurements. To avoid this problem, the presentinvention can replace the interpolating resistors with inductivecomponents (such as ferrite chip inductors). At low frequencies (forcesensing scan) these would act as resistors. At high frequencies(capacitive scan) these would increase their impedance and block thecapacitive signals from passing. Another way to accomplish this would beto use small ICs instead of the resistive networks between adjacentactive lines. The ICs could switch between a resistive mode, where theinterpolating lines are hooked up to each other via resistors and acapacitive mode, where the interpolating lines are disconnected fromeach other or where each active line connects to several adjacentinterpolating lines. In all of these cases, the present invention wouldpreserve the high resolution and interpolation of the resistive scan. Inthe capacitive scan mode, the scan resolution would reduce back down tothe active line resolution. Another challenge with this approach is thatthe presence of the FSM could interfere with capacitive scanning.Luckily, when users are not touching or touching only lightly, theresistance of the FSM is high. Thus, the capacitive scan mode would beminimally affected. Furthermore, the present invention could switchbetween resistive and capacitive scan modes in different areas of thesensor. In areas where no touch is detected, the scan could switch tocapacitive mode. In areas where a touch is detected, the scan mode couldswitch to resistive.

In the case where it is desired to combine capacitive touch, IFSA, and adisplay, a display can also be placed in between a transparentcapacitive touch sensor and a non-transparent IFSA sensor, creating atouch display with both the hover and light touch capability ofcapacitive touch and the precision and force sensitivity of IFSA.

Other configurations using transparent IFSAs are possible, where boththe capacitive sensor and the IFSA sensor (or a sensor combining bothelements) are placed on top of the display.

Magnetic/Electromagnetic Sensing

Because IFSA sensors are transparent to magnetic fields, it is possibleto place an electromagnetic sensor such as an electromagnetic resonance(EMR) sensor (often used for stylus tracking) below the IFSA sensor andsense through it. It is also possible to place RFID/NFC reader/writercoils below the sensor, since RFID/NFC works in a similar way by sendingelectromagnetic pulses to an RFID/NFC tag/transceiver. Because magneticfields can be used to transmit power, it is also possible to use coilsbelow an IFSA sensor to transmit power to a nearby device. In fact, allof these technologies (EMR, RFID, NFC, and wireless power) can becombined since they all use one or more conductive coils to generate amagnetic field. In the remainder of this section, the present inventionwill refer to technology that enables EMR/RFID/NFC sensing as just EMRsensing.

By combining EMR sensing with IFSA, it becomes possible not only todetect the location and force of objects on top of the sensor, it alsobecomes possible to uniquely identify objects which have an EMR/RFID/NFCtag/transceiver. It also becomes possible to transfer power or databetween the objects and the sensor. These objects can include thingslike keyboards, computer mice, buttons, sliders, knobs, styli, and evenmobile phones and tablets. By placing multiple EMR/RFID/NFC transceiversinto these objects, it becomes possible to sense not just the positionbut also the orientation of the objects (for example, with a stylus, ifa transceiver is put into both the tip and eraser sides, it is possibleto tell whether the user is writing or erasing).

Also, it is possible to combine the information from the IFSA sensor andthe EMR sensor to extract additional information. In the case of astylus, for example, by comparing the position of the stylus touch andthe position of the EMR transmitter, it is possible to determine thetilt angle of the stylus. It may also be possible to combine the signalof an EMR sensor and an IFSA sensor to improve overall accuracy and/orperformance. This is possible because the EMR sensor may have better“relative” tracking performance (in other words, it may be better atmeasuring a small change in position), while the IFSA sensor may havebetter “absolute” tracking performance (in other words, it may have amore accurate estimate of an object's position, but may not be able toaccurately measure very small movements). This is because EMR sensorscan be affected by the presence of ferrous objects and external magneticfields, which typically do not affect IFSA sensors.

Because an EMR sensor is typically manufactured on a PCB layer, it ispossible to combine the bottom PCB used for an IFSA sensor with the PCBused for the EMR sensor, creating a 3-4 layer PCB with bothfunctionalities. Another way to combine an IFSA sensor with an EMRsensor is to pattern one portion of the EMR sensor (containing row orcolumn magnetic coils) on one unused side of the IFSA sensor and topattern the other portion of the EMR sensor on the other unused side ofthe IFSA sensor. This is most conveniently done on a thru-mode IFSAsensor, where both the top and bottom substrate have one unused side.

The sensor combination with IFSA and EMR can also be placed below adisplay to create a touch-screen with the added capabilities allowed byan EMR sensor since both EMR signals and IFSA signals are not blocked bya display. Alternatively, it is possible to place a transparent IFSAsensor on top of a display while placing an EMR sensor below thedisplay.

Optical Sensing

Optical sensing technologies have been demonstrated that can trackfingers or objects optically. Some of these technologies work byshooting light beams across the surface and detecting when one or moreof the beams is interrupted. Others use an array of emitters andreceivers and detect light that bounces off of a user. This type ofsensor can even be integrated into a display such as an OLED or LCDdisplay. Other technologies use a camera to see the location of user'shands. Also, various ingenious designs have been shown that can compressthe optical path of these types of sensors into thin films and evendisplay backlights.

The IFSA sensing technology can be integrated with many of these opticalsensing technologies either by placing the IFSA below the optical sensoror by placing a transparent IFSA on top of the optical sensor. Some ofthe optical sensing technologies described are good at sensing hover andproximity, but can not accurately detect when a touch has actuallycontacted a surface or the force of a touch. This can be especially truein outdoor environments, where bright sunlight can interfere withoptical sensor operation. The output of the IFSA sensor and opticalsensor can be combined to create a combination that is more robust andcan track objects above the touch surface, accurately detect contactwith the surface, and measure the force applied to the surface.

Combination of Capacitive, Electromagnetic, and Optical Sensors

All four technologies (IFSA, EMR, capacitive, and optical touch) can becombined together to get all the features of these technologies (forcesensing, hover and light touch, tracking/powering of EMR/NFC/RFIDtransceivers) in a single sensor. As described previously, these sensorsmay share various layers in the stackup to reduce cost and thickness.These can also be combined with displays to create new user interfaces,hardware devices, and unique user experiences.

Characteristics and Advantages

In addition to having high accuracy, scalability to large sizes, andper-touch force sensitivity, the present invention has many otherdesirable characteristics. First, sensors based on the present inventionare insensitive to electrical noise, thus they do not requiresignificant electrical shielding and can operate robustly in manyenvironments. This also reduces the amount of filtering and postprocessing that must be done on the signals, which reduces thecomplexity of the analog circuits and filtering algorithms, and reducespower consumption.

Present invention sensors provide a high dynamic range of forcesensitivity from several grams to several kilograms of force per touchpoint. Unlike capacitive sensors, the present invention sensors cansense any object, such as a plastic stylus, and not just conductiveobjects such as human fingers. It can also sense the fingers of userswho are wearing gloves, or who have very rough skin.

The present invention greatly simplifies the design process. Thetouch-separation resolution and the touch tracking resolution of thepresent invention sensors can be controlled separately and can easily betuned to the demands of a particular application. A given sensorconfiguration can be increased or decreased in size without changing thesensor characteristics, thus a particular sensor design can be appliedto a wide range of products, reducing design cost, and time to market.Furthermore, even the shape of the present invention sensors can bechanged without changing the sensor performance. For example, arectangular sensor design can be easily modified to produce round,oblong, donut, peanut shaped sensors, and any other shape that can bemapped to a two-dimensional surface. The modified sensor will have thesame performance (including touch-tracking accuracy and forcesensitivity) as the original rectangular sensor design.

The present invention sensors can be wrapped around non-flat surfaces,and can even be manufactured directly on the exterior surfaces ofdevices using a variety of different manufacturing methods. The sensorsmay even be incorporated into textiles and soft materials.

The present invention sensors can be manufactured with straightforwardmanufacturing processes which include standard rigid or standardflexible printed circuit board (PCB) manufacturing methods which usuallyinvolve a subtractive process or printed electronics (PE) methods whichinvolve the printing of conductive inks using additive processes. Onemajor advantage of the ability to build the sensor on a rigid orflexible PCB is that all the sensing electronics (as well as otherelectronics) can be directly attached to the same PCB substrate as thesensor itself using a standard process such as SMT (surface mount). Theelectronics can be placed on the same surface as the sensor, or can bemounted on the backside of the sensor surface. Also, some components(for example resisters) can even be embedded into the sensor substrate.Alternately, the sensor can be added to a pre-existing circuit boarddesign that may have other functionality besides being a sensor. Forexample, one could take a TV remote or game controller PCB (whichalready has a PCB with discrete buttons), a microcontroller,transmitter, and other circuitry and add an IFSA sensor area to thatsame PCB with minimal design changes.

The scanning electronics do not need any exotic components and can bebuilt either with off the shelf parts or with an application specificintegrated circuit (ASIC). In many cases, the scanning electronics canbe implemented with a single microcontroller and some small andinexpensive discrete components (such as resistors and capacitors).

Compared with other touch technologies, the present invention technologyis inherently low power and supports many ways to reduce that powerfurther. For example, the present invention supports multi-resolutionscanning, which allows the user, or the software using the sensors, toreduce scan resolution, while at the same time increasing speed andreducing power consumption in real time. The sensor design also supportseven lower power modes with reduced functionality which can detect thepresence and/or rough location of a single or multiple touches withouthaving to perform a full scan of the sensor. The present inventionsupports very fast frame rates for applications that require fastfeedback or response, such as musical instruments.

Finally, the present invention is robust and can be designed to survivethe stringent environmental requirements of consumer, military,automotive, and industrial electronics. Because it senses force ratherthan changes in capacitance, it can operate in the presence of water orother fluids, and can be hermetically sealed, permitting it to functionunderwater and in the most hostile environments.

Exemplary Application Contexts

The sensors presented in the present invention can be used for manydifferent applications. These applications fall into categories whichinclude general purpose multi-touch input, replacing simpler discretecontrols such as buttons or sliders, and measuring pressuredistributions. In the first category are applications such as phone,tablet, laptop, and display touch panels and also writing pads,digitizers, signature pads, track pads, and game controllers. In thesecond category are applications in toys, musical instruments (such aselectric pianos, drums, guitars, and keyboards), digital cameras, handtools, and replacing dashboard controls on automobiles and othervehicles. In the third category are applications inscientific/industrial measurement (such as measuring the shape orflatness of a surface), medical measurement (such as measuring thepressure distribution of a person's feet or their movement in a bed),and robotics applications (such as coating a robot with sensors to giveit the ability to feel touch and contact).

Furthermore, there are many other applications beyond the ones that arelisted, and many applications may use the sensors in differentmodalities. For example, in some applications a sensor could be used asa general purpose input, a set of simple controls such as buttons orsliders, and as an area pressure sensor. These different uses could besimultaneous, could be separated in time, or could be separated in space(different areas of the sensor behave in different ways). Moreimportantly, the different uses of the sensor can all be enabled insoftware, giving the designer/developer an incredible level offlexibility in the way that they use the sensor.

In user interface applications, the present invention sensors areextremely useful because they can distinguish between a light touch anda press. In direct manipulation interfaces such as smart phones ortablets, light touch is often used by users when they are moving theirfingers from one area to another, scrolling, sliding, or want moreinformation about an on-screen item. Heavy touch can be used fordragging, selection, activation, and engagement of a control.Furthermore, different levels of heavy touch can be used to modulate thestrength/amplitude of an interaction. In indirect manipulationapplications such as track pads, writing pads, and digitizer pads, lighttouch can be used for moving a cursor onscreen and hovering over an itemto get more information, while heavy touch can be used (as a clutch) fordragging, selection, activation, or manipulation. Finally, pressure canbe used to gauge user intent. For example, in applications wherephysical controls are simulated such as buttons, sliders, and knobs (forexample, when emulating a keyboard, a recording mixer, or a genericcontrol panel), the controls can ignore light touch in order to allowthe user to comfortably rest their hands on the interface withoutaccidentally activating anything.

Because of the high accuracy of the present invention sensors, they canbe used to capture fine motion. This is very important in applicationssuch as tracking a stylus with high precision to enable writing,drawing, sketching, painting, calligraphy, and other interactionsinvolving a stylus. A soft layer can be added above or below the sensorto create a nicer surface feel and to further improve tracking accuracy.The present invention sensors can be combined with displays. This can bedone either by creating a transparent sensor and layering it on top ofthe display, by incorporating the technology into the substrate of thedisplay itself, or by layering the sensor behind the display and feelingforce through the display. This works especially well with flexibledisplays.

The present invention sensor can also be combined with other sensingtechnologies. For example, a capacitive touch sensor can be placed ontop of the present invention sensor to enable the detection of hoverabove the surface and extremely light touch.

Because the present invention sensor is transparent to magnetic fields,a magnetic/electromagnetic sensor, such as an EMR sensor, can be placedbelow the present invention sensor to enable the detection/tracking ofstyli or other devices with active or passive magnetic/electromagnetictags. A display can also be layered into any of these stack-ups. Thecombination of these different sensor technologies can enable richerinteractions.

Because the present invention sensors feel pressure, and pressure iseasily transferred through most deformable surfaces, the presentinvention sensors can also be embedded below a variety of deformablesurfaces. For example, they can be embedded underneathflexible/deformable floors, under flexible robot skin, or under paint ona wall. They can be embedded into the surfaces of tables, or onto matsthat lay on top of tables.

The present invention sensors can also be used to add sensing to unusedsurfaces. For example, they can be placed on the back of a phone,tablet, or game controller to allow extra degrees of interaction bytouching the back of the device.

Visual feedback on the screen can be used to give the users a sense ofwhere and how hard they are touching.

Sensors can also be placed on the back of a digital watch or other smalldevices, where space for a user-interface device is extremely limited,thereby increasing the available touch-area without increasing the sizeof the device.

The present invention sensor can be manufactured on a flexiblesubstrate, allowing them to be embedded into flexible devices.

Some example applications include creating a flexible phone or aflexible tablet, using the sensor in the wristband of a digital watch orbracelet, and putting the sensor into the sole of a shoe or sneaker orinto clothing to track a user's motions, detect impacts or provide aportable user-interface.

The present invention sensors can also be designed such that they can becut or folded to wrap around complex surfaces such as a robot fingertip.Or, they can be directly manufactured onto complex surfaces. In short,almost any surface can be imbued with touch sensitivity by layering oneof the present invention sensors on, behind, or inside of it.

Exemplary Tablet Interface Embodiment (6500)-(8000) Tablet Form FactorOverview (6500)-(7600)

While the present invention may be embodied in a wide variety of formsbased on application context, one preferred exemplary inventionembodiment as applied to a tablet form factor. This user interfacecontext is generally depicted in the views of FIG. 65 (6500)-FIG. 76(7600). Here the tablet user interface (assembled in FIG. 65 (6500) anddepicted in the assembly view of FIG. 66 (6600)) is comprised of atablet base (FIG. 67 (6700)) that supports a printed circuit board (PCB)(including the VIA and associated control electronics) (FIG. 68(6800)-FIG. 69 (6900)), pressure membrane (FIG. 70 (7000)), overlay(FIG. 71 (7100)), and covering bezel (FIG. 72 (7200)) with backlit LOGOindicia.

This exemplary embodiment of the invention as depicted in FIG. 65(6500)-FIG. 66 (6600) is designed to target applications indesktops/laptops or tablet user interfaces. For desktop/laptop use, itwill typically be used by connecting it to a computer via the USB port.For tablet use, it will typically be charged and/or configured via theUSB port, but transmit data via Bluetooth/Bluetooth LE. The device maybe designed to magnetically latch to a tablet/tablet cover, and couldhave interchangeable and possibly back-lit overlays.

Assembly View (6600)

As generally depicted in FIG. 66 (6600), the assembly stack for thispreferred exemplary embodiment incorporates a base (FIG. 67 (6700)),PCB/battery (FIG. 68 (6800)-FIG. 69 (6900)), membrane (FIG. 70 (7000)),overlay (FIG. 71 (7100)), and bezel (FIG. 72 (7200)).

Base (6700)

As generally depicted in FIG. 67 (6700), the base for this preferredexemplary embodiment will preferably be made of a rigid material such asaluminum, with alignment pins (6701, 6702, 6703, 6704) utilized to helpalign the layer stack comprising the tablet system.

PCB/Battery (6800)-(6900)

As generally depicted in FIG. 68 (6800)-FIG. 69 (6900), the PCB(6910)/Battery (6920) layer includes the following:

-   -   Area (6911) for microcontroller, analog sensing circuits,        power/battery management, BLUETOOTH® radio, USB TX/RX, and other        electronics;    -   Micro-USB connector (6912);    -   Sensor active-area (6913);    -   Battery (Li-Poly or similar power source) (6920); and    -   Alignment holes (×4) (6931, 6932, 6933, 6934).

Force Sensing Membrane (7000)

As generally depicted in FIG. 70 (7000), the force sensing membranelayer includes the following:

-   -   Substrate (such as PET or KAPTON®);    -   Force-sensing material such as FSR on the underside of the        substrate; and    -   Alignment holes (×4).

Overlay (7100)

As generally depicted in FIG. 71 (7100), the overlay may be pliable,with a slippery upper surface. It is anticipated that overlays may beswappable, with different graphics, or tactile relief patterns. Overlaysare also anticipated in some configurations to be back-lit or side-lit.

Bezel (7200)

As generally depicted in FIG. 72 (7200), the covering bezel may includethe following:

-   -   Graphic/logo, which can be a light-pipe, and may be back-lit        with constant or changing illumination patterns;    -   Opening for the overlay; and    -   Opening for a USB port or other communication interface.

Mechanical Properties (7300)-(7600)

As generally depicted in the sectional and detail views of FIG. 73(7300)-FIG. 76 (7600), while mechanical construction may vary widely, itis anticipated that some preferred invention embodiments may beconfigured to a thickness of approximately 4.25 mm. The reducedcomplexity of the electronics needed to monitor the VIA results in areduced area required for electrical components and battery capacity andas such may result in some configurations being significantly thinnerthan competing technologies.

The device may be held together by clasps between base and bezel andthin adhesive layers between base and PCB, PCB and membrane, andmembrane and bezel. The overlay may be configured to simply drop in ormay have some means of coupling to the base cavity, which may includemagnets or clasps.

Exemplary Touch Pad Schematic/Layout (7700)-(8000)

The exemplary construction application context as generally illustratedin FIG. 65 (6500)-FIG. 76 (7600) may be implemented using amicrocontroller and PCB as generally depicted in the schematic blockdiagram of FIG. 77 (7700) and PCB layout of FIG. 78 (7800) (top copper),FIG. 79 (7900) (bottom copper), and FIG. 80 (8000) (via pads). Thislayout generally depicts a typical VIA array that is mated with apressure sensitive material and embedded in the tablet form factor asgenerally illustrated by FIG. 65 (6500)-FIG. 76 (7600). The schematicdepicted in FIG. 77 (7700) makes use of conventional microcontrollertechnology with integrated host computer communications (USB, I2C, SPI,wireless (BLUETOOTH®, BLUETOOTH LE®, other 2.4 GHz interface, etc.),UART), ADC inputs, general purpose digital I/O (GPIOs) in conjunctionwith GPIO expanders and multiplexers to implement the column drivers androw sense circuitry depicted in this document.

Capacitive Interpolation Sensor (8100)-(8800) Overview

Yet another embodiment of the present invention may utilize theinterpolation concepts associated with the FSA in the context of acapacitive sensor array as depicted in FIG. 81 (8100)-FIG. 88 (8800).The designs depicted in these drawings describe two exemplaryconfigurations:

-   -   single-sided diamond pattern with bridges (as generally depicted        in FIG. 81 (8100)-FIG. 82 (8200)); and    -   double-sided with straight rows and columns (as generally        depicted in FIG. 83 (8300)-FIG. 84 (8400)).

These two designs are specifically targeted for transparent capacitivesensors. This type of sensor typically resides between a display and aprotective upper layer (such as a plastic film or glass layer). Theremay also be transparent shielding layers between the sensor and thedisplay. Note that in the case of the diamond-patterned sensor, it couldalso be flipped upside down and then laminated to the display. In thiscase, the substrate could become the layer that the user touches. In thecase of the double-sided sensor, the two sides (rows and columns) couldbe printed on separate substrates, and the substrates could then belaminated together. In this case, it is not possible to do the sametrick of flipping the sensor upside down, to have one of the substratesact as the touch-surface.

Single-Sided Diamond Pattern with Bridges (8100)-8200)

As generally depicted in FIG. 81 (8100)-FIG. 82 (8200), a capacitorsensor employing a single-sided diamond pattern is illustrated that isformed on a substrate (8101) such as glass or plastic. In this preferredembodiment, conductive bridges (8102) (with dielectric below to avoidshorting with columns) are formed between transparent conductors (8103)(such as ITO, carbon nanotubes, conductive polymer, nano-wires,patterned conductor, etc.) to form the VIA. This array is attached tocolumn (8104) and row (8105) interpolation resistors formed either bydepositing a resistive material or simply by leaving a thin bridge ofthe transparent conductor on the substrate (8101) surface. These IIC andIIR resistors (8104, 8105) are electrically coupled via column (8106)and row (8107) connections to active column trace lines (8108) andactive row trace lines (8109). These column (8108) and row (8109) tracelines are routed to areas (8110) for bonding conductive flexes whichinterconnect with drive and sense electronics (or in some casesconfigured for directly bonding electronics to the substrate (8101).

Referring to the sectional view of FIG. 82 (8200), the substrate (8201)is seen supporting the column transparent conductors (8203) and rowtransparent conductors (8213). A dielectric layer (8212) separates thecolumn transparent conductors (8203) and row transparent conductors(8213) and supports the conductive bridges (8202). Also depicted in thiscross section are the row trace connections (8207) and row traces (8209)that may be formed using etched or printed conductive material.

Double-Sided Pattern with Straight Row/Columns (8300)-(8400)

As generally depicted in FIG. 83 (8300)-FIG. 84 (8400), a capacitorsensor employing a double-sided pattern with straight rows and columnsis illustrated that is formed on a substrate (8301) such as glass orplastic. In this preferred embodiment, columns (8302) and rows (8303)are on opposite sides of the sensor (so they do not short) and mayalternatively be deposited onto separate substrates (one for rows andone for columns). The columns (8302) and rows (8303) are formed oftransparent conductors (such as ITO, carbon nanotubes, conductivepolymer, nano-wires, patterned conductor, etc.) to form the VIA. Thisarray is attached to column (8304) and row (8305) interpolationresistors formed either by depositing a resistive material or simply byleaving a thin bridge of the transparent conductor on the substrate(8301) surface. These IIC and IIR resistors (8304, 8305) areelectrically coupled via column (8306) and row (8307) connections toactive column trace lines (8308) and active row trace lines (8309).These column (8308) and row (8309) trace lines are routed to areas(8310) for bonding conductive flexes which interconnect with drive andsense electronics (or in some cases configured for directly bondingelectronics to the substrate (8301).

Referring to the sectional view of FIG. 84 (8400), the substrate (8401)is seen supporting the column transparent conductors (8402) and rowtransparent conductors (8403). Also depicted in this cross section arethe row trace connections (8407) and row traces (8409) that may beformed using etched or printed conductive material.

Sensor Manufacturing

One advantage of both of these designs is that they can be manufacturedwith the same exact process currently used to make capacitive touchsensors. The main difference is that this invention embodiment adds thein-between (interpolating) rows and columns and changes the mask patternfor the transparent conductive material (usually ITO) to create littleconductive lines, which act as the interpolating resistors. Theresistance can be adjusted by changing the width of these lines. Besideschanging the mask patterns (and possibly some changes to the testprocedures), there are no extra steps involved in manufacturing thesecapacitive sensors.

Capacitive Sensor Advantages

The advantage of an interpolating capacitive sensor based on thisdisclosed design is that it has much better linearity than aconventional capacitive sensor. This results in:

-   -   much better touch and stylus tracking without needing to        calibrate the sensor;    -   better estimation of touch shape and area;    -   better signal; and    -   the ability to use much thinner cover-glass/plastic between the        user's finger and the sensor, allowing for much thinner devices.

The last point is very important in the construction of mobile/portabledevices such as tablets, cellphones, smartphones, and the like.

For an opaque capacitive sensor, it is possible to use one of thesedesigns, and incorporate the use of one of the IFSA conductor patternsdiscussed previously, and just remove the force sensing material. Theforce sensing material would typically be replaced with a dielectricsuch as a thin plastic film or glass in this application.

Exemplary Cup Pressure Profiles (8500)-(8800)

An example of the present invention as applied to a pressure sensortablet form factor is depicted in FIG. 85 (8500) wherein a drinking cupis contacted with the pressure sensor tablet surface. FIG. 86 (8600)depicts a profile of the sensed pressure without interpolation and thegrid associated with the TSM read out from the TSA along with detectedpressure regions. FIG. 87 (8700) depicts an approximate reconstructionof the forces seen by the individual force sensing elements in the VIAobtained by performing an upsampling operation of the TSM. FIG. 88(8800) depicts the individual detected ellipse data computed by the CCDbased on the TSM data depicted in FIG. 86 (8600). Note that the TSM dataas illustrated in FIG. 86 (8600) can be used to reconstruct the finedetail as seen in the upsampled data depicted in FIG. 87 (8700) and togenerate the discrete regions of detection in FIG. 87 (8700) andellipses in FIG. 88 (8800).

Exemplary Paintbrush Pressure Profiles (8900)-(9200)

An example of the present invention as applied to a pressure sensortablet form factor is depicted in FIG. 89 (8900) wherein a paintbrush iscontacted with the pressure sensor tablet surface. FIG. 90 (9000)depicts the pressure profile of the TSM obtained by the CCD by scanningthe TSA. FIG. 91 (9100) depicts the associated pressure regions detectedbased on the pressure profile. FIG. 92 (9200) depicts the individualdetected ellipse data computed by the CCD based on the TSM data depictedin FIG. 90 (9000).

As can be seen from this example, the pressure sensor VIA is bothsensitive and capable of detecting shape/ellipse data associated withindividual areas of the contact region. This example also depicts theextreme sensitivity of the system using the interpolation techniquestaught by the present invention.

Capacitive Touch Sensor Description (9300)-(12500) Overview ofInterpolating Capacitive Sensor Circuits

The main benefit of interpolating force-sensing sensors that have beendescribed above is that it is possible with these configurations toincrease the linearity of the sensor and its ability to track touches ata higher resolution than the resolution of the active electronics. Thesame is true for interpolating capacitive sensors. Although mostexisting capacitive sensors already have some level of interpolation(due to the fact the electric field lines spread through the spacearound the sensor), capacitive sensors tend to have very non-linearinterpolation behavior. This is problematic in cases where highprecision is important, especially for use to detect touch input orstylus input. Currently, designers of existing capacitive touch sensorsdeal with this non-linearity by creating look-up tables whichnumerically map non-linear sensor (X,Y) positions into a linear space.However, these look-up tables are typically created under one set ofconditions and cannot fully compensate for the non-linearity of thesensors under all conditions.

Using the techniques taught by the present invention it is possible toincrease the resolution of a capacitive sensor without needing toincrease the number of drive and sense lines in the electronics. Doingthis creates a much more linear and predictable sensor response,yielding much better finger touch and stylus performance. However, thereare some differences between the techniques used to add interpolation toa force-sensing sensor and a capacitive sensor as described below.

Interpolation Resistor Values (9300)

In the case of interpolating force-sensing sensors, the presentinvention targets a resistance of approximately 1KΩ between active linesto achieve the desired interpolation behavior (for a sensor with threeinterpolation resistors between each pair of active lines such as thesensor in FIG. 33 (3300), the value of each interpolation resistor wouldbe 1K/3=333Ω).

For interpolating capacitive sensors, it may be generally determinedthat a resistance of 1KΩ between active lines on the receive side is toolow, causing a very low signal at the receive side of the sensor.Experimentation has determined that a resistance of 10KΩ between activelines on the receive side provides a much stronger signal (for a sensorwith three interpolation resistors between each pair of active linessuch as the sensor in FIG. 93 (9300), the value of each interpolationresistor would be 10K/3=3.3KΩ).

Generally, it has been found by experimentation that higher resistors onthe receive side yielded a higher signal. However, at a certain level,higher resistances cause the sensor itself to begin acting as a low-passRC filter, thus resistances much higher than. 10K between active linesmay cause signal loss. Higher resistance on the transmit side reducespower consumption, but similarly may cause RC losses if they get toohigh. Both experimental and analytical approaches can be used to findthe optimal transmit and receive resistor values for given sensorconfiguration.

Scanning the Sensor

The main difference between scanning a force-sensing interpolatingsensor and a capacitive interpolating sensor is that for a capacitiveinterpolating sensor, the present invention optimally sends and receivesan AC or oscillatory waveform such as a square wave or a sine wave,while for a force-sensing interpolating sensor, the present inventionoptimally sends and receives DC signals.

As a result, it is only required that the sensor system employ differentcircuitry to generate and capture the signal. This circuitry isdescribed in later sections.

Sensor Behavior

In the case of interpolating force-sensing sensors, the received signalis generally at ground potential or close to ground potential when noforce is applied, and increases as a user applies force.

In the case of interpolating capacitive sensors, the received signal isgenerally highest when no touches are applied. This is due to thecapacitive coupling between row and column electrodes. When a finger orother conductive object approaches the sensor, conductive paths arecreated for the electric field lines emanating from the transmit portionof the sensor through the user's body to ground. This causes a reductionin the signal received on the receive electrodes. Thus, the signalstarts out high, and reduces as the user approaches. Experiments havedetermined that interpolating capacitive sensors have very littlesensitivity to force. They mostly respond to the shape and area of eachtouch or conductive object in contact with the sensor.

Processing Sensor Data

Software algorithms similar to those described for interpolatingforce-sensing sensors can be used to detect the baseline level forinterpolating capacitive sensors to baseline away (subtract) the signallevel when no touches are detected. Because all of the processingalgorithms described previously depend on a signal strength thatincreases from zero when a touch is detected, the signal from theinterpolating capacitive sensor can be inverted by subtracting thesignal received from the sensor from the measured baseline. Thiseffectively inverts the sign of the signal such that a touch results ina positive increase in the signal. This allows all the later stages ofprocessing to deal with a signal that increases where there are touches,thus allowing all the touch-processing algorithms described forinterpolating force sensing sensors to work on the signal produced byinterpolating capacitive sensors without significant modification.

Capacitive Transit Electronics

As previously mentioned, an interpolating capacitive sensor must bedriven with AC or oscillatory waveforms. These are usually in the formof square or sine waves. In the following sections, various methods areproposed for generating these waveforms. Note that these methods can beused as part of a capacitive sensor or within an active stylus togenerate a signal.

Square Wave Generation

In order to generate a square wave, one can use a standard PWM modulefound on most modern microcontrollers (MCU). These PWM modules can beused to generate a periodic control signal inside the microcontroller.When combined with a standard GPIO module, it is possible to create asquare wave output on a GPIO at a fixed frequency. This frequency can betuned by the firmware, as PWM modules are often capable of generating awide range of frequencies. Unfortunately, the output voltage is usuallylimited to logic level (1.8V-5V) for the given microcontroller. Toincrease SNR, it is desirable for the amplitude of the transmittedsignal to be as high as possible. Therefore, it is beneficial to use thePWM output as a control signal for circuitry that can generate highervoltage levels.

Square Wave Generation Using a PWM With an Analog Mux (10000)

FIG. 100 (10000) shows how a PWM module can be paired with an analog muxto generate a high-voltage square wave output. Basically, the analog muxtakes two voltages (a high voltage and a low voltage) and uses the PWMas a control signal. The PWM signal muxes between the high and the lowvoltage levels, creating a high-voltage square wave with the samefrequency as the PWM. The frequency used in many preferred inventionembodiments is 200 Khz, but other frequencies can be chosen as well. Thefrequencies can also be varied dynamically to reduce susceptibility toexternal noise or in cases where it is desirable to transmit multiplefrequencies at the same time.

This circuit allows the present invention to decouple the voltage levelsof the MCU from the voltages levels that are used to drive the sensor.VHigh can be higher than the voltage that the MCU operates on. Inaddition, VLow can be lower than the ground level of the MCU. Forexample, while a typical MCU may operate at 3.3V or 1.8V, the presentinvention may use a VHigh of +5V and a VLow of −5V, resulting in atransmitted signal with an amplitude of 10V. As an alternative example,the present invention can use an even higher “high voltage” of 12V and alow voltage of 0V, resulting in a signal with an amplitude of 12V.

Square Wave Generation Using a PWM With a Comparator (10100)

FIG. 101 (10100) shows an alternative method for generating ahigh-voltage square wave. In this configuration, the PWM output is fedinto the non-inverting input of an operational amplifier (OPAMP). TheOPAMP is configured to be a comparator, which means that the output willbe VHigh when the PWM signal is greater than Vref, and the output willbe VLow when the PWM signal is lower than Vref. As depicted in thediagram, the waveforms are nearly identical to the waveforms seen inFIG. 100 (10000). R1 and R2 form a simple voltage divider to createVref. In most practical applications, R1 will be equal to R2, which willcreate a Vref at VDD/2 (as seen in the “PWM Signal Output” graph in FIG.101 (10100).

Sine Wave Generation

At times, it can be advantageous to transmit sine waves instead ofsquare waves. Square waves are made up of several different frequencies,while a sine wave is a single frequency. When driving an interpolatingcapacitive touch sensor, it is possible to drive multiple electrodes atthe same time. If each electrode is driven with a different frequency,then the receive side can determine how much energy was received of eachfrequency, and thus determine the contribution from each driveelectrode. Driving with a sine wave instead of a square wave makes thesignal cleaner and easier to filter and interpret on the receive side.For example, sine waves can be better filtered with low-pass, high-passand band-pass filtered and can be decomposed using algorithms such as anFFT.

Sine Wave Generation Using an Oscillator (10200)

There are various ways to generate a sine wave. One way is by building aphase-shift oscillator, as can be seen in FIG. 102 (10200). The outputof the OPAMP is fed into a series of filters which shift the phase ofthe output by 180 degrees. This causes a condition where the OPAMPexperiences positive feedback and begins to oscillate. The output ofthis stage will be a sine wave. The R and C values in the circuit can betuned to select a specific oscillation frequency. In FIG. 102 (10200), avoltage buffer is placed at the output of the oscillator to preventloading of the oscillator stage by the sensor electrode. This allows theoscillator to be tuned without having to worry about the specific inputimpedance characteristics of the sensor it is driving. An analog mux isadded to the output to enable/disable the transmission of the sine wave.Feedback mechanisms can be added to allow on-the-fly variation of thefrequency generated by the oscillator circuit.

Sine Wave Generated Using a High-Speed DAC and Amplifier (10300)

Phase-shift oscillators are fairly straightforward to build, but theyhave several drawbacks. Temperature changes can greatly affect theresistance values in the feedback loop, which will cause the frequencyto drift. Also, there is not an easy way to reliably enable/disable theoscillator in an efficient manner (oscillators often take time tostabilize when they are first enabled).

Therefore, it is often advantageous to generate sine waves with adigital approach. FIG. 103 (10300) shows a sine wave generationtechnique that uses a digital-to-analog converter (DAC) to generate adigital representation of a sine wave. In this implementation, a DACperipheral is using direct memory access (DMA) to read values out of asine wave lookup table in memory (the memory must be preloaded with adigital representation of a sine wave). The DAC takes these digitalvalues and converts them to analog (as seen in the “DAC Output”waveform). The DAC output, however, cannot be used directly to drive anelectrode. This is because the signal created by a DAC is often jagged,since the DAC is converting discrete values (causing a discretestaircase effect). Thus, it may be beneficial to low-pass filter the DACoutput to create a smoother sine wave signal. After this filter, thesignal can be used to drive an amplifier, which boosts the amplitude ofthe signal used to drive the electrode, thereby increasing the SNR ofthe system. In this circuit, a transmit enable signal is used toenable/disable the DAC.

One of the biggest benefits of this approach is that it allows thecircuit to easily select the desired transmit frequency and amplitudethrough software. This can be useful in cases where frequency hopping isused to avoid noise, or in cases where it is desirable to transmitmultiple frequencies simultaneously on different electrodes or even thesame electrode.

Capacitive Receive Electronics

As previously mentioned, an interpolating capacitive sensor must detectAC or oscillatory waveforms. These are usually in the form of square orsine waves. In the following sections, various methods are proposed fordetecting these waveforms. Note that these methods can be used as partof a capacitive sensor or within an active stylus to detect oscillatorysignals.

Receive Circuit Using a Preamp, Rectifier, and Integrator (10400)

Since the present invention transmits AC frequencies to drive theinterpolating capacitive sensor, the receive electronics must be able toreliably detect the strength of a received AC signal. In a system thatis using a single transmit frequency, it is possible to build an ACdetector circuit as shown in FIG. 104 (10400). This circuit takes areceived AC signal and converts it to a DC signal that can be read by anADC. This resulting DC voltage level indicates the strength of thereceived AC signal. This is accomplished through a multi-stage signalprocessing approach as described below.

The first stage is a simple RC filter that is used to rejecthigh-frequency noise. The filter is optional, as it may not be needed ininstances where the noise is low enough. The cutoff frequency for thisfilter can be chosen so that only the desired frequency ranges arepassed through. For this particular circuit configuration, the presentinvention transmits a 200 KHz frequency for the transmit signal.Therefore, the component values selected were R1=1000Ω and C1=100 pF.This yields a cutoff frequency of about 1.6 MHz. It is important to notethat this filter does not necessarily have to be an RC low-pass filter,as depicted in the figure. One skilled in the art can use a high-passfilter, band-pass, or notch filter to combat various noise profiles. Apassive filter is used here in order to simplify the components neededin the circuit. This filter can be replaced with an active filter tomore effectively reject noise.

After this first filter stage, the signal is fed into a non-inverting,variable-gain amplifier (preamp). For this particular circuitconfiguration, R2=100Ω and R3=10 KΩ are chosen for this example. SinceR3 is a variable resistor, it is possible to achieve variable gain up toa maximum of 101×. It is important to select an operational amplifier(U1) with a sufficient Gain-Bandwidth Product (GBP). For this circuitconfiguration, the GBP is 25 MHz. This means that for a gain of 101,this amplifier stage has a bandwidth of about 248 KHz, which will allowthe present invention 200 KHz signal to pass through. In practice, it isusually not required that the full gain of the amplifier at this stage,so a GBP of 25 Mhz is more than enough at this stage. An invertingamplifier can be used in this stage as well, since the polarity of theamplified signal does not significantly affect the later stages.

After the preamp stage, another optional filtering stage is illustrated.In this configuration, R4=1KΩ and C4=510 pF are chosen, which yields acutoff of 312 KHz. As mentioned before, this filter could be replacedwith an active filter and could be a high-pass, band-pass, or notchfilter.

After the second filter stage, the signal is fed into a half-waverectifier. This stage blocks the positive side of the waveform, andallows only the negative side to pass through. This allows feeding thesignal into the final stage, an integrator. Before the rectifier, thesignal is charge-balanced. If the full version of the signal were fedinto an integrator, the result would yield zero (the sum of charge aftereach period of the waveform would be approximately zero). Blocking thepositive side of the waveform provides an unbalanced signal that can beproperly integrated. Note that the reason that the present inventiononly passes the negative side of the signal is that the integrator is aninverting integrator, and it is desirable that the integrator to producea positive signal. In the case of a non-inverting integrator, one wouldchange the polarity of the half-wave rectifier to allow the positiveside of the waveform to pass through.

As already mentioned, the final stage is an analog integrator. It isimportant to note that this integrator has negative gain. By feeding ina negative signal from the rectifier, the output of the integrator willbe positive. This allows use of ADCs that are only able to samplepositive voltages. For this circuit configuration, R6=100Ω, R7=100Ω, andC7=10 nF are chosen. C7 is a variable capacitor, which allows changingof the charge rate of the integrator. For the integrator stage, it isimportant to select an operational amplifier (U2) that is unity-gainstable. Otherwise, the integrator will be unstable and the output mayoscillate.

SW1 is an analog switch that can be closed/opened by a signal generatedfrom a GPIO on the CCD. Most standard analog switches can be used forSW1. For instance, Texas Instruments makes the TS12A4516, which isperfect for this application. When SW1 is closed, the charge that isstored by the integrator capacitor is cleared. This in essence resetsthe integrator. This switch is an important part of the AC signaldetector. SW1 must stay closed (integrator is in reset) when selectingwhich row that is connected to during a scan. This prevents integratingany switching noise that gets through the first few stages of thiscircuit. Once the correct row is connected to the input of the ACdetector, SW1 is opened to start integrating. This gives the mostreliable ADC reading for each row.

In FIG. 104 (10400), an ADC Sample Window is also shown on theintegrator output waveform. For an integrator, the output settles to aDC value when there is no voltage at the input. For this system, afinite number of cycles from the transmit side of the sensor areintegrated. Therefore, after receiving the fixed set of pulses, theintegrator output will settle to a DC value. This is where the signal issampled with the ADC. After the ADC sampling is complete, the integratoris reset and the circuit is made ready to receive the next row.

For this circuit, it is important to note that two parameters can changeto tune system performance (R3 and C7). The amount of signal receivedoften depends on the configuration of the sensor this circuit isconnected to. Therefore, for a given sensor, R3/C7 must be adjustedaccordingly. Typically, the signal will be highest when there is nothingin contact with the sensor, and will decrease when a finger approachesthe sensor. To maximize the dynamic range of signal values captured bythe ADC it is desirable that the signal that is output by the integratorwhen there is no touch to be at the upper range of the ADC withoutclipping. Furthermore, it is desirable to make sure that neitheramplifier is being pushed beyond its gain bandwidth product. R3 and C7can be adjustable either manually (by tuning a variableresistor/variable capacitor), can be adjustable in the design stage, orcan be adjustable digitally via software.

Multi-Frequency Receive Circuit with Preamp and High-Speed ADC (10500)

It is important to note that the circuit in FIG. 104 (10400) is not ableto distinguish multiple received frequencies. In the case where multiplefrequencies need to be captured on a single receive electrode, it ispossible to use the approach depicted in FIG. 105 (10500). This circuitis an amplifier that feeds into a high-speed ADC. This high-speed ADCmust have a sampling rate higher than 2× the maximum transmit frequencyused in the system. One skilled in the art will know that this is tokeep the sampling frequency above the Nyquist rate, which eliminatesalias effects in the captured signal. In order to capture at such a highrate, it is usually necessary to have an ADC capturing the waveformthrough a direct memory access (DMA) interface. This allows the ADC towrite captured values directly into memory without requiring dedicatedCPU cycles.

Software algorithms can then be applied to the signal to performfiltering (for example high-pass, low-pass, band-pass or notch filteringin software) and to detect the amplitude of signals at the transmittedfrequency or frequencies. In some circumstance, this approach can beadvantageous over the previous approach, even in cases where just onefrequency needs to be detected, because it eliminates the rectifier,which cuts the amplitude of the captured signal in half, and because italso eliminates the integrator, which can be difficult to tune and cansaturate if the input signal is too high.

Multi-Frequency Separation of Frequencies Using an FFT (10600)

Once the waveform is accurately captured, it is possible to run an FFTalgorithm (FIG. 106 (10600)) in order to convert the signal from thetime-domain into the frequency-domain. This will reveal which particularfrequencies make up the received signal and also indicate how muchenergy was received in each frequency band. In FIG. 106 (10600), it canbe seen that the FFT reveals that the received signal is made up of fourfrequencies (F1, F2, F4, and F4), and it is possible to see the strengthat which each was received.

Digitally capturing the signal and performing an FFT makes it possibleto simultaneously drive a sensor on multiple columns with differentfrequencies and to reconstruct digitally the contribution of the signalwhich comes from each column. It also allows the sensor to determinefrequencies at which there is excessive electrical noise and tofrequency hop to other channels which may have less noise.

Scanning a Capacitive Sensor

Scan Circuitry with Single Transmitter/Receiver (9300)

FIG. 93 (9300) shows scanning circuitry that supports scanning aninterpolating capacitive sensor one active row-column intersection at atime.

Exemplary Scanning Method for Single Transmitter (11600)+(11700)

An exemplary method for scanning this type of sensor is shown in FIG.116 (11600), with the appropriate sub-routines detail defined in FIG.117 (11700).

Scan Circuitry with Single Transmitter/Multiple Receivers (9400)

FIG. 94 (9400) shows scanning circuitry that supports scanning multiplerows of an interpolating capacitive sensor simultaneously. Instead ofhaving all the active rows connected to a single AC Signal Detector andADC, there are multiple instances of the AC Signal Detector and ADCs.Analog switches allow each AC Signal Detector and ADC to connect to morethan one active row. (Texas Instruments part TS12A12511 or a similarpart with the appropriate number of throw terminals would work well forthis).

Exemplary Scanning Method for Multiple Receivers (11600)+(11700)

The method for scanning this type of sensor is the same as the methoddepicted in FIG. 117 (11700) for a sensor with a single transmitter andreceiver, however, for each scan cycle, multiple AC Signal Detectors canbe connected to multiple active sense electrodes and multiple ADCsamples can be taken, reducing overall scan time.

Scan Circuitry with Multiple Transmitters (Multiple Frequencies) (9500)

FIG. 95 (9500) shows scanning circuitry with multiple transmitters onthe column lines. Using this circuitry, it is possible to transmitdifferent frequencies simultaneously on different columns, and toreconstruct, for a given row, the contribution of the signal coming fromeach active column.

To reconstruct the signal contribution from each active column, multiplesamples of the signals must be collected by the ADC over time. Then, anFFT can be applied to the signal to determine the amplitudes at eachtransmitted signal. These signal amplitudes can then be mapped back tothe column positions at which they were generated and written to a TSM.Alternatively, multiple AC Signal Detectors, tuned to differentfrequencies can be used in parallel to detect multiple frequencies.However, this may be prohibitive from a power and cost standpoint.

If there is only a single AC Signal Amp/Filter in the system, thisprocedure can be performed once for each row until the entire capacitivesensor profile is reconstructed. Furthermore, it may be advantageous todrive only a subset of columns simultaneously, to allow more separationbetween frequencies and more spatial separation between driven columns.In this case, the Column Multiplexing Circuitry can be used to groundthe columns which aren't being actively driven. Then, several passeswith different combinations of driven and grounded columns can beperformed to reconstruct the entire capacitive sensor profile.

Exemplary Scanning Method for Multiple Transmitters (11600)+(11800)

The method for scanning this type of sensor is shown in FIG. 116(11600), with the appropriate sub-routines defined in FIG. 118 (11800).

Scan Circuitry with Multiple Transmitters/Receivers (MultipleFrequencies)

Taking this one step further, it is possible to use multipletransmitters on the columns and multiple receivers on the rows as shownin FIG. 95 (9500) to scan a two-dimensional array of sensor elementssimultaneously. In this case, multiple transmitters can simultaneouslytransmit different frequencies, while multiple receivers simultaneouslysample multiple rows. Then FFTs can be applied to the signals at eachrow to reconstruct the different contributions at each row from thetransmitters at each column and to reconstruct a two dimensional arrayof signal values.

As mentioned in the previous description, it may be advantageous todrive a subset of columns and/or to scan only a subset of rowssimultaneously. In this case, all the other rows and/or columns can beattached to ground using the Column and Row Multiplexing Circuitry.Then, several passes can be performed with different driven Row/Columncombinations to reconstruct the entire capacitive sensor profile. As anexample, in FIG. 95 (9500), it can be seen by looking at the state ofthe Column and Row Multiplexing Circuitry, that all the Columns arebeing driven simultaneously, while only every other row is being scannedsimultaneously.

Supporting Active Stylus

Capacitive touch sensors can generally be used with one of three typesof stylus. The first type of stylus attempts to mimic the capacitiveproperties of a human finger. These types of styli are typically made ofconductive material and have a big, squishy (pliable), rubber tip. Thedownside of this type of stylus is that they are very imprecise and itis difficult to do palm-rejection with this type of stylus since it isdifficult to determine which touch is coming from the stylus and whichtouch is coming from a finger/palm.

The second type of stylus is an active stylus which automaticallysynchronizes to the transmit circuitry of the sensor, and generates aninverse signal to the signal the sensor expects. These types of styliessentially mimic the capacitive signature of a finger. Because these donot need any special mode of communication with the capacitive sensor,no additional discussion of these types of active styli is presentedhere.

The third type of stylus is an active stylus which is able tocommunicate with the sensor to determine its location relative to thesensor grid. This type of stylus can be configured to transmit data tothe sensor, receive data from the sensor, or to do both. The advantageof this approach is that an active stylus using one of these approachescan achieve much greater accuracy, and that this kind of active stylusis easy to distinguish from a finger or palm, allowing the user to resttheir hand on the surface of a sensor while using the stylus andfacilitating other types of interaction. The rest of this sectiondescribes ways of implementing this type of active stylus with aninterpolating capacitive sensor.

Synchronization of Sensor and Stylus

In order to support an active stylus, it may be important to synchronizethe sensor with the stylus. If a sensor is sending signals to a stylus,the stylus needs to know where in a particular scan the sensor is at agiven time. If a stylus is transmitting a signal, the sensor needs toknow when to activate its receive circuitry. Furthermore, if the stylusattempts to transmit while a sensor is just scanning for touches, thismay cause unwanted electrical noise and may confuse the sensor. Thus, anactive stylus which transmits should have a way of only transmittingwhen the sensor is looking for the stylus. Synchronization methods willbe discussed in the following sections for each of the different typesof scans.

Performing a Stylus Scan (12400)

FIG. 124 (12400) depicts the interaction between and active stylus andan interpolating capacitive sensor. Because the sensor generally onlycommunicates with one stylus at a time, a full matrix scan is notnecessary for detecting the position of a stylus. Instead, to determinethe position of the stylus, the present invention needs only todetermine its X position and its Y position. To determine the Xposition, one scan along the columns may be performed, measuring thesignal strength between each active column and the stylus. Aninterpolation algorithm can then be used to determine the coordinate ofthe stylus along the X axis. Next, the same procedure can be performedalong Y, this time measuring the signal strength on each active row tothe stylus. FIG. 124 (12400) shows the amount of coupling between thestylus and the sensor in the form of two graphs (one below and one tothe right of the sensor). In the configuration where the stylus istransmitting and the sensor is receiving, the dots on the graph indicatethe amount of signal that is received at each active electrode (along Xand Y). In a configuration where the sensor is transmitting and thestylus is receiving, the dots indicate the amount of signal the styluswill receive from each active electrode.

Because this type of scan only needs to be done along active columns androws (instead of all the active column-row intersections), this type ofscan can be performed very quickly (much faster than scanning formultiple touches). Furthermore, because stylus latency is much morenoticeable than finger latency, and because writing and sketchinginvolves very fast and precise motions, this type of scan can beperformed at a higher frequency than scans for fingers.

Stylus Interpolation Algorithm

Because an active stylus receives/transmits signals to the VIAwirelessly, a non-zero signal strength will typically be detected foreach active row and active column of the sensor (FIG. 124 (12400)).However, the signal strengths reported for rows/columns that are faraway from the position of the stylus at a given point in time aregenerally very low. For example, note that the bottommost active row ofFIG. 124 (12400) has a very low signal. Thus, before computing theinterpolated X or Y position, the present invention must first determinewhich signals should be interpolated.

In one preferred exemplary approach, two neighboring locations with thetwo strongest signals and the two additional locations adjacent to those(four locations in total) are used to compute an interpolated position.Referencing FIG. 124 (12400), it can be seen that active columns 2 and 3have the strongest signals. The two neighboring locations are activecolumns 1 and 4. Thus, active columns 1, 2, 3 and 4 will be used in thiscase to compute the X stylus location. Similarly, along the rows, activerows 2 and 3 have the strongest signals and their neighbors are activerows 1 and 4. Thus active rows 1, 2, 3 and 4 will be used in this caseto compute the Y stylus location.

To compute the X and Y location, the weighted average position of thefour selected columns is computed, where the weight is the signalstrength. The interpolated position is computed as the sum of the fourpositions multiplied by their respective signal strengths divided by thetotal of the signal strengths at the four locations. The formula isthus:InterpolatedPosition=(Position1*SignalStrength1+Position2*SignalStrength2+Position3*SignalStrength3+Position4*SignalStrength4)/(SignalStrength1+SignalStrength2+SignalStrength3+SignalStrength4)

As an example, since the signal strengths of the selected active columns1, 2, 3 and 4 in FIG. 124 (12400) are 0.1, 0.5, 0.8, and 0.25respectively, the interpolated X position is computed as:(1*0.1+2*0.5+3*0.8+4*0.25)/(0.1+0.5+0.8+0.25)=2.73. Since the signalstrengths of the selected active rows 1, 2, 3 and 4 are 0.15, 0.6, 0.6,and 0.15 respectively, the interpolated average Y position is computedas (1*0.15, 2*0.6, 3*0.6, 4*0.15)/(0.15+0.6+0.6+0.15)=2.5.

Stylus Tip Sensor

One challenge with an active stylus as described so far is that it maybe difficult to determine whether the stylus is in the air or touchingthe sensing surface. The reason for this is that the stylus willcontinue to transmit/receive signals from the sensing surface even whenit is above the sensor, and it may be difficult to determine purely fromthe signals whether the stylus is touching the surface or not.Furthermore, in the case of a purely capacitive touch sensor, it may bedifficult to determine the amount of force that is being applied to thestylus.

To address this problem, a tip sensor may be included in the stylus todetermine whether the stylus is in contact with the sensor surface andto determine the amount of force exerted onto the stylus by the user.There are many known ways to implement this type of tip sensor such as aswitch, an optical force sensor, a capacitive force sensor, a resistiveforce sensor, an inductive force sensor, etc.

Information about whether the stylus is touching and the amount of forceexerted on the tip can be relayed via BLUETOOTH® wireless communicationsor via a signal transmitted from the stylus to the interpolatingcapacitive sensor. This information can be used in application softwareto (for example) change the darkness or width of a stylus strokerendered to the screen.

In addition to a sensor at the tip, the stylus may have other sensorsembedded in the body or on the other end, in the form of an “eraser”.All of these types of sensors can be implemented in a similar fashionand can transmit data to/from the device via BLUETOOTH® wirelesscommunications or via a signal transmitted from the stylus to theinterpolating capacitive sensor.

Stylus Hover

In cases where the stylus is not in contact with the surface, it may bepossible to determine the approximate stylus position and height abovethe sensor. This can be extremely useful in applications where a displayand a touch sensor are not co-located, allowing a user to see where thestylus is before touching it down. It is also useful for implementingvirtual drawing tools such as an airbrush (since real air-brushes applypaint when in the air above the surface being painted).

The position of a hovering stylus can be simply determined in the sameway as the position for a stylus that is touching the sensor. The heightcan be determined by looking at the total signal strength received atthe four X and Y active columns and rows with the highest signals(described previously). For a stylus in contact with the surface of thesensor, the sum of these signal strengths is typically constant. As thestylus moves away from the surface of the sensor, the sum of the signalstrengths will decrease in a repeatable manner. The relationship betweentotal signal strength and height above the sensor surface can bemeasured analytically, and then stored in a lookup table, which can beaccessed at runtime to compute the height of the stylus above the sensorsurface.

Multiple Styli

Multiple active styli can be used with an interpolating capacitivesensor either simultaneously (two or more styli used at the same time),or non-simultaneously (the user can have many different active styli,but use them only one at a time).

Because each stylus has a receiver/transmitter, communication betweenmultiple styli and a given interpolating capacitive sensor can besequenced in time, so that each stylus can have a chance to determine anX/Y position separately. Furthermore, each stylus can have a unique ID,communicated via BLUETOOTH® wireless communications or transmitted fromthe stylus tip to the interpolating capacitive sensor. The unique ID canbe used to give different styli different functions, such as differenttip shapes, different colors, or different user identities (the devicecan determine which user is writing based on which stylus is beingused). Alternatively, communications between multiple styli and theinterpolating capacitive sensor can occur in different AC frequencybands.

Multiple Receivers/Transmitters

A single stylus can have multiple receivers/transmitters (which will bereferred to as transceivers), allowing finer grained determination ofstylus orientation. For example, if there are two transceivers at thetip next to each other, stylus rotation can be determined based on therelative (X,Y) positions of the two transceivers. Alternatively, ifthere are two transceivers, one above the other, near the tip, stylustilt can be determined by determining the relative (X,Y) positions ofthe transceivers, as well as the height of the upper transceiver. Therecan also be transceivers on the back-side of the stylus, to support anerase feature.

Sensor Circuitry/Method for Transmission to Stylus(9600)+(11900)+(12000)

FIG. 96 (9600) depicts a circuit configuration in which the sensortransmitted AC signals to a stylus which is configured to receive thesesignals. An exemplary method associated with this scanning circuitry isillustrated in FIG. 119 (11900), with sub-routines further defined inFIG. 120 (12000).

The sensor/stylus interaction is as follows. First, the sensor andstylus must synchronize with each other. To accomplish this, the sensortransmits a unique synchronization frequency on all of the sensorrows/columns at the same time. The stylus waits until it detects thepresence of this particular frequency. This marks the beginning of ascan. After the sensor sends its synchronization beacon, the sensorconnects one active electrode at a time to the AC Signal Source andtransmits a predetermined number of pulses to the electrode. Since thestylus and sensor are synchronized, the stylus knows how long eachelectrode transmission will take.

The stylus goes into receive mode while the sensor is transmitting, andconverts the signal receive strength into a digital value using a methodlike that shown in FIG. 104 (10400). The stylus logs the receivestrength of the signals from each electrode that it received during thescan. After the scan is complete, the stylus can send the raw data tothe sensor over BLUETOOTH® wireless communications or other similarwireless data channel so that the sensor can process the data andcalculate the position of the stylus. In another embodiment, the styluscan internally compute its own position using its on-boardmicrocontroller and send the computed position to the sensor.

Alternatively, synchronization can be performed by using BLUETOOTH®wireless communications. This is due to the fact that the BLUETOOTH®wireless communications transmitter and receiver need accurate timesynchronization, and this same synchronization can be used to generate acommon time-base and schedule between the stylus and the sensor, whichcan be used to synchronize the signals sent on each column and row. Yetanother way to perform synchronization is for the sensor to send asynchronization pulse sequence for each row/column being scanned. Thesequence can be encoded using Amplitude Modulation, FrequencyModulation, Phase Modulation or other known modulation scheme.

Sensor Circuitry/Method for a Transmitting Sensor (9700)+(11900)+(12100)

In this configuration, the stylus will be transmitting AC signals to thesensor, which is configured to receive these signals (see FIG. 97(9700)). The method for this scan is illustrated in FIG. 119 (11900)with subroutines defined in FIG. 121 (12100).

In this exemplary embodiment, the stylus can be in a low power modeuntil the sensor is ready to scan for the stylus. This prevents thestylus from transmitting during a scan for touches. When the sensor isready to start a stylus scan, the sensor can signal to the stylus tostart transmitting pulses using the BLUETOOTH® wireless communicationsconnection.

The stylus will emit a predetermined number of pulses at a periodicinterval. Since the sensor knows how long each of these pulses takes,the sensor can electrically couple each active electrode in turn up tothe AC Signal Detector, and receive while the stylus should betransmitting. The sensor will generate a list of received signalstrengths that can be used to calculate the position of the stylus.After the scan, the sensor can instruct the stylus to go back into a lowpower mode until it is time for the next scan.

Sensor Circuitry/Method for Bidirectional Stylus (9800)

The previous two methods can be combined to allow bi-directionalcommunication between the stylus and the sensor as shown in FIG. 98(9800). To enable this, the interpolating sensor requires a set of ACsignal transmitters and detectors on both the columns and rows and thestylus, similarly, requires a set of AC signal transmitters anddetectors for the stylus tip. One advantage of this configuration isthat bi-directional synchronization can be performed without BLUETOOTH®wireless communications. Furthermore, triangulation can be performed bytransmitting a signal from the sensor to the stylus, from the stylus tothe sensor, or in both directions. This can be used to increase theaccuracy of the triangulation.

Other Types of Objects with Active Tracking

The transceiver circuitry presented here for active tracking of a styluscan be applied to other types of objects. For example, they may beembedded into paint-brushes, rulers, toys, even into thimbles, to allowtracking of those objects of the interpolating capacitive sensorsurface.

Combining Force Sensing and Capacitive Sensing

Force/Capacitive Sensing Circuitry (9900)

All of the force-sensing sensor configurations shown earlier (FIG. 41(4100) FIG. 64 (6400)) can be scanned both with a DC signal to measureapplied force and with an AC signal to measure capacitive coupling. FIG.99 (9900) shows a circuit diagram which details the electronicsnecessary to scan a sensor both with AC and with DC signals. It alsoshows a sensor VIA where each of the sensor elements acts as both avariable resistor and a variable capacitor.

It has been determined experimentally that in sensors which have anon-continuous force-sensing layer (such as shown in FIG. 41 (4100)-FIG.42 (4200), FIG. 46 (4600), FIG. 48 (4800), FIG. 49 (4900) and FIG. 50(5000)-FIG. 60 (6000)) the electric field lines are able to pass throughthe force sensing layer and can be affected by fingers and conductiveobjects. Thus, it is possible to operate the sensor both as a capacitivesensor (sensing light contact by conductive objects) and as a resistivesensor (sensing pressure from any object).

It has been determined by experimentation that in sensors that have acontinuous force-sensing layer (such as shown in FIG. 43 (4300) and FIG.47 (4700)), it is not possible to detect conductive objects (since theforce sensing layer tends to block the electric field lines). However,in some cases, it is possible to detect lighter forces with the ACsignal before a change in the DC signal is seen. This is because therecan be a minute air-gap between the layers of the sensor, and thecapacitive scanning approach is essentially able to measure the distanceof the air gap before there is enough contact to cause a change inconductivity between the layers.

The circuit diagram shown in FIG. 99 (9900) can be configured to scanthe sensor with a DC signal by enabling the DC Voltage Source anddisabling the AC Signal Source, and switching the analog switch(TS12A12511 or equivalent) to receive signal from the DC SignalConditioning circuit. Alternatively, the circuit can be configured toscan the sensor with an AC signal source by enabling the AC SignalSource, disabling the DC Voltage Source, and switching the analog switchto receive signal from the AC Signal Detector. The circuit can beswitched between these two modes either on a per-scan basis or for eachsensor element that is scanned.

Force/Capacitance Sensing Methods (12200)-(12300)

FIG. 122 (12200) shows a method for performing a full resistive scanfollowed by a full capacitive scan. FIG. 123 (12300) shows the secondapproach which involves performing both a resistive and capacitivemeasurement for each sensor element during a scan.

Advantages of Combining Force Sensing and Capacitive Sensing

When a sensor has the ability to sense force and capacitance changes, itbecomes possible to use the data from each scan together to improvesensor performance. Combining the two scans together allows forhigher-accuracy feature extraction and improves touch tracking. Methodsfor achieving this will be described in the following paragraphs. Notethat although it is possible to combine the raw data from each scan, itis much more practical to run the contact tracking algorithms (describedearlier in this document) on the raw data from each scan and combine thecontact data sets afterwards. Therefore, the following discussion willfocus on the methods for combining force and capacitive sensing contactdata.

The force and capacitive scans each generate an array of values (TSM).As discussed earlier in this document, contact data can be extractedfrom each of these arrays. After this contact extraction, the remainderleft is a list of contacts detected by the capacitive sensor, and a listof contacts detected by the force sensor. For each capacitive scancontact, it is possible to calculate the distance of this contact toeach of the contacts from the force scan. Using a simple distancethreshold, it is possible to decide if these contacts come from the sameobject interacting with the sensor. This distance calculation/matchingprocess can be done for all the capacitive scan contacts. Thisessentially generates a list of paired contacts (although some contactswill not have a match). After this matching process is complete, ahigh-level list of contacts may be generated and produce a indication ifa contact was found in the capacitive scan, the force scan, or bothscans.

Sensor States (12500)

FIG. 125 (12500) shows how one can use this data to learn more about theobjects interacting with the sensor. Since there are two possible statesfor two sensor types for a given object, there is a total of fourpossible states for each object:

STATE 1: The object is NOT detected by the resistive force sensor andthe object is NOT detected by the capacitive sensor. If an object doesnot activate either of the sensors, there are likely two possibilities.The first is that there is actually no object interacting with thesensor. The second is that there is a non-conductive object hoveringclose to the sensor.

STATE 2: The object is NOT detected by the resistive force sensor andthe object is detected by the capacitive sensor. In this state, it isknown that the object is made of some type of conductive material, sinceit is detected by the capacitive touch sensor. Also, it is known thatthe object is either hovering or contacting the sensor with a very lightforce (since the force sensor is not activated).

STATE 3: The object is detected by the resistive force sensor and theobject is detected by the capacitive sensor. In this state, it is knownthat the object is made of a conductive material and that the object isexerting a force on the sensor (not hovering).

STATE 4: The object is detected by the resistive force sensor and theobject is NOT detected by the capacitive sensor. In this state, it isknown that the contact is made of a non-conductive material and that theobject is exerting a force on the sensor (not hovering).

FIG. 125 (12500) also shows state changes for common types ofinteractions. Path A shows the state transitions for a conductive object(i.e., fingertip) touching the sensor. If the scan rate is sufficient, afinger touch will always transition from state 1 to 2 to 3. If scanningat a lower frame rate, it may be possible to transition from state 1 tostate 3. As the touch lifts off of the sensor, the state will changeback to 1 (either directly or via state 2).

Path B shows the state changes for a conductive object (i.e., fingertip)that is hovering above the sensor, but never touches the surface. Thisoccurs if someone is interacting with the sensor exclusively throughhover.

Path C shows the state changes for a non-conductive object touching thesensor. It is generally not possible to detect non-conductive objectswith the capacitive sensor, so it is not possible to detect a hoverstate for these objects.

Being able to tell what type of material objects are made of can be veryvaluable. For example, if a person is using a non-conductive stylus todraw on a sensor, it is possible to clearly distinguish a user's handfrom the stylus (since skin is conductive). The contacts for the usershand will be in state 3, while the contact from the stylus will be instate 4. This permits correct identification of the stylus, which isimportant for drawing applications that require correct identificationof a stylus vs. palm. State 2 is also a very important for sensorusability. For many capacitive touch solutions on the market, it is verydifficult to distinguish hover from an actual touch. Vendors of existingcapacitive touch solutions often use a signal-strength threshold wherethe hover turns into a touch. However, during actual use, this thresholdcan often end up being too low, resulting in inadvertent touches (beforea user finger even contacts the screen), or the threshold can be toohigh (resulting in a screen that is unresponsive to touch). By combininga capacitive sensor with a force sensor, it is possible to easilydistinguish these two hover vs touch states (state 2 vs. state 3).

Improving Accuracy

When conductive objects interact with the sensor (i.e., fingers), it isactually possible to improve the accuracy of the sensor by combining thecapacitive and force data. When the conductive object is in contact withthe sensor, the object will create two contacts (one with the forcesensor data and one with the capacitive sensor data). It is possible totake these two contacts and average them together to yield a moreaccurate result. Averaging these two readings will make the finalcontact less susceptible to instantaneous noise from a reading and inmost cases will make the result more accurate.

Furthermore, when touches are extremely light, the capacitive signal mayyield a more accurate touch position. In situations where the accuracyof these extremely light touches is important, it may be preferable touse just the touches extracted from the capacitive signal or to use aweighted average to combine the capacitive and force signal, where thecapacitive signal is weighted more than the force signal.

Conversely, there may be cases when the force signal may be stronger orcleaner than the capacitive signal. This can happen when the device isexposed to moisture, strong electrical noise, or if a fine-tipped objectsuch as a metal stylus is used. In these cases it may be preferable touse just the touches extracted from the force signal or to use aweighted average to combine the capacitive and force signal, where theforce signal is weighted more than the capacitive signal.

The detection of the conditions where one signal (force or capacitive)is weaker or noisier than the other can be performed automatically insoftware, and the software can then automatically compensate by usingjust the cleaner signal or by giving more weight to the cleaner signal.

Self-Capacitive Sensing

Many existing capacitive touch sensors use a combination ofmutual-capacitive scanning and self-capacitive scanning to detect thepositions of touches. While most of the scan algorithms described hereinfor capacitive sensors fall into the category of mutual-capacitivescanning, the present invention sensors can also be scanned with aself-capacitive approach.

The main difference between a mutual-capacitive scan and aself-capacitive scan is that a mutual-capacitive scan looks for thepresence of a touch at each row/column intersection, whileself-capacitive scan looks for the presence of a touch either at a givenrow or at a given column. This is similar to the one-dimensional scanthat has been described for interpolating force-sensing sensors in thatthe position of touches can be determined either along the X or the Yaxis. This is also similar to the one-dimensional scan methods used todetermine the (X,Y) position of a stylus.

Self-capacitive scanning can be performed in a very similar way forinterpolating capacitive sensors as the one-dimensional scan forinterpolating force-sensing sensors. For each column/row on which it isdesired to measure self-capacitance, ground all the neighboringcolumns/rows must be grounded and then the capacitance of the desiredrow/column measured.

One way to measure this capacitance is to use a circuit such as the oneshown in FIG. 98 (9800). This figure depicts both an AC Signal Sourceand an AC Signal Detector on both rows and columns. To measure thecapacitance of a row/column using this circuit, it is a simple matter totransmit an AC signal and receive it on the same row/column while theneighboring rows/columns are grounded. As a finger or other conductiveobject approaches the driven row/column, the capacitance will increase,causing the magnitude of the detected signal to decrease.

Alternately, dedicated capacitance measuring modules, which areavailable from a variety of different manufacturers, and areincorporated into many available microcontrollers can be used in placeof the combination of an AC Signal Source and AC Signal Detectors inFIG. 98 (9800) to measure the capacitance of a given row/column.

Multi-Resolution Capacitive Scan

Just as with interpolating force-sensing sensors, interpolatingcapacitive sensors support the ability to scan at multiple resolutions.This can be used to improve scan speed, save power, and implementmulti-resolution scan. This can also be very useful when scanningobjects of different size. For example, a lower resolution scan can beused for scanning for fingers and a higher resolution scan can be usedfor scanning for styli.

Just as with interpolating force-sensing sensors, lower resolution scanscan be achieved by setting a subset of the active electrodes in a VIA toa high impedance state, and scanning just the remaining activeelectrodes. This is accomplished by setting the switches in the columnmultiplexing circuitry and the row multiplexing circuitry in FIG. 93(9300)-FIG. 99 (9900) to the NC (not connected) state. This effectivelycreates a sensor with lower active line resolution, but still preservesthe linearity of the sensor and the accuracy with which a touch can betracked.

Force Sensing Capacitive (10700)

While the interpolating sensor embodiments shown so far have either usedchanges in resistance to measure force, or changes in capacitance todetect touch, it is also possible to create a sensor that uses changesin capacitance to measure force. This can be done by taking a capacitiveinterpolating array with electronics such as shown in FIG. 93 (9300) toFIG. 98 (9800) and structure such as shown in FIG. 81 (8100)-FIG. 84(8400) and modifying the structure such that each sensor element at eachrow-column intersection of the VIA changes capacitance in response toforce. One possible embodiment of this is shown in FIG. 107 (10700).

FIG. 107 (10700) shows a lower layer, consisting of an interpolatingcapacitive sensor array, an upper layer which consists of a deformablesurface and a squishy (pliable) layer in between. The bottom side of theupper layer is coated with a conductive material. This conductive layercapacitively couples with the capacitive sensor array in the same waythat a finger couples with the capacitive sensing arrays in FIG. 81(8100)-FIG. 84 (8400). However, as pressure is applied, the middlesquishy (pliable) layer deforms, allowing the upper layer to come closerto the capacitive sensor array. As this happens, the capacitive couplingbetween the conductive layer and the transmit lines increases, causing adecrease in the signal on the receive lines. This causes a decrease inthe signal received on the receive lines, and this change varies inresponse to the deformation of the top layer, which changes based onamount of pressure exerted by the user.

In cases where it is desirable to have a transparent sensor, forapplications such as integration with a display, the entire sensorstructure can be made transparent by using transparent materials in thewhole stackup. For example, the top layer can be made of either plasticor thin, flexible glass. A transparent conductive material such as ITO,carbon nanotubes, silver nano-wires, fine-wire mesh, or transparentconductive polymer can be used to form the conductive layer on theunderside of the top layer. The middle layer can be formed from atransparent squishy (pliable) material such as silicone, polyurethane,or a transparent gel.

To improve electrical isolation, the conductive layer on the undersideof the top layer can be electrically connected to ground.

Integration with Display and Other Sensor Types (10800)

Transparent capacitive sensors can be integrated with displays such asLCD, OLED, or electrophoretic displays by laminating or attaching thesensor to the top of the display. FIG. 108 (10800) shows an example of acapacitive sensor on top of a display. A protective top surface can beattached above the touch sensor to protect both the sensor and thedisplay.

In some cases, it may be desirable to add additional sensors to thecombined stackup. FIG. 108 (10800) also shows one alternative embodimentwhere an electromagnetic sensor is attached below the display. Thissensor may be used to sense the presence of a special electromagneticstylus, RFID tags, or to wirelessly transmit power/data between otherdevices in contact with the screen.

Interpolating Capacitive Compared with Prior Art (10900)-(11500)

Compared to existing capacitive sensors which do not have interpolation,the present invention sensors can track fingers and styli with very highprecision and linearity. In FIG. 109 (10900) and FIG. 110 (11000) a topdown view and a cross section of a typical prior art capacitive touchsensor (without interpolation) are depicted. Note that the activeelectrode pitch is 4 mm, and that the pitch of the sensing pattern isalso 4 mm. Looking at the cross section in FIG. 110 (11000), it can beseen that only a small set of electric field lines intersect with thefinger, and the pattern of these lines is highly non-linear. As thefinger moves in a straight line across the surface of the sensor in FIG.109 (10900), the path that the sensor thinks the finger has taken iswavy and non-linear as illustrated by the thick curvy line. This is dueto the inherent non-linearity of the sensor, and while many capacitivesensor designs attempt to compensate for this non-linearity with lookuptables, it is impossible to compensate well for all sizes and shapes oftouch.

In FIG. 111 (11100) and FIG. 112 (11200) a top down view and a crosssection of an exemplary present invention interpolated capacitive touchsensors are depicted. Note that although the active electrode pitch isstill 4 mm, the addition of interpolation elements allows for a muchtighter sensing pattern pitch of 1 mm (with typical present inventionrow/column pitches range from 0.25 mm to 2.5 mm). Looking at the crosssection in FIG. 112 (11200), one can see that many more electric fieldlines intersect with the finger, causing many more capacitiveinteractions over the surface of the finger and therefore a much morelinear response. As the finger moves in a straight line across thesurface of the sensor in FIG. 111 (11100), the path that the sensorthinks the finger has taken is very linear and has very fewimperfections as illustrated by the thick curvy line. This more linearresponse is due to the higher pitch of sensor elements in theinterpolated sensor, and this increased linearity benefits allinteractions with the sensor, whether the user uses their finger, astylus, or any other conductive object. Furthermore, any imperfectionsin the finger position are very small in scale, and can easily befiltered using a time-domain filtering algorithm applied to thecalculated finger positions to get a perfectly linear line at theoutput.

Note that the present invention interpolating approach gives similarperformance benefits with other capacitive sensor configurations. Forexample, an interpolating capacitive sensor with a grid pattern, such asthe one shown in FIG. 83 (8300)-FIG. 84 (8400) will also track astylus/touch with more accuracy than a sensor with a grid pattern thatdoes not support the present invention interpolation method.

In FIG. 113 (11300)-FIG. 115 (11500), a comparison is depicted betweenthe signal obtained from an existing touch sensor built by a majortouch-sensor manufacturer (MICROCHIP® Technology, Inc., 2355 WestChandler BLVD, Chandler, Ariz. 85224-6199 USA) and the signal obtainedfrom a present invention sensor, using a 4 mm active line pitch and a 1mm sensing pattern pitch. FIG. 113 (11300) shows the signal for a singletouch picked up by a MICROCHIP® sensor (which is indicative of othercapacitive touch sensors). Here it can be seen that the signal is verynon-linear. The central element has a very high peak, and thesurrounding elements fall off very quickly. FIG. 114 (11400) shows thesignal from the present invention interpolated capacitive touch sensorfor a single touch. Here it can be seen that the signal has a muchsmoother profile, better matching the profile of the finger touching it.Furthermore, in FIG. 115 (11500), depicts an upsampled reconstruction ofthe signal to estimate the signal picked up by the individual sensorelements. Here, it can be observed that it is possible to reconstructthe actual shape of the finger touch. This type of reconstruction is notpossible for the signal produced by the MICROCHIP® sensor because of theinherent non-linearity in its signal.

System Summary

The present invention system anticipates a wide variety of variations inthe basic theme of construction, but can be generalized as a touchsensor detector system comprising:

-   -   (a) touch sensor array (TSA);    -   (b) array column driver (ACD);    -   (c) column switching register (CSR);    -   (d) column driving source (CDS);    -   (e) array row sensor (ARS);    -   (f) row switching register (RSR);    -   (g) analog to digital converter (ADC); and    -   (h) computing control device (CCD);

wherein

-   -   the TSA comprises a variable impedance array (VIA) comprising        VIA columns and VIA rows;    -   the VIA comprises capacitance elements interlinking the VIA        columns and the VIA rows;    -   the VIA is configured to electrically couple a plurality of        interlinked impedance columns (IIC) within the TSA with a        plurality of interlinked impedance rows (IIR) within the TSA;    -   the IIC further comprises a plurality of individual column        impedance elements (ICIE) electrically connected in series        between the VIA columns;    -   the IIR further comprises a plurality of individual row        impedance elements (IRIE) electrically connected in series        between the VIA rows;    -   the ACD is configured to select the IIC within the TSA based on        the CSR;    -   the ACD is configured to electrically drive the selected IIC        using the CDS;    -   the ARS is configured to select the IIR within the TSA based on        the RSR;    -   the ADC is configured to sense the electrical state of the        selected IIR and convert the electrical state to a sensed        digital value (SDV);    -   the electrical state is determined by the sum of current        contributions of variable impedance elements within the VIA,        where the current contribution of each element is determined by        a voltage divider formed between the columns of the VIA, a        current divider formed between the rows of the via, and the        state of the impedance element, to produce a sensed current for        a given row-column intersection with the VIA; and    -   the CCD is configured to sample the SDV from the ADC at a        plurality of positions within the TSA to form a touch sensor        matrix (TSM) data structure.

This general system summary may be augmented by the various elementsdescribed herein to produce a wide variety of invention embodimentsconsistent with this overall design description.

Method Summary

The present invention method anticipates a wide variety of variations inthe basic theme of implementation, but can be generalized as a touchsensor detector method wherein the method is performed on a touch sensordetector system comprising:

-   -   (a) touch sensor array (TSA);    -   (b) array column driver (ACD);    -   (c) column switching register (CSR);    -   (d) column driving source (CDS);    -   (e) array row sensor (ARS);    -   (f) row switching register (RSR);    -   (g) analog to digital converter (ADC); and    -   (h) computing control device (CCD);

wherein

-   -   the TSA comprises a variable impedance array (VIA) comprising        VIA columns and VIA rows;    -   the VIA comprises capacitance elements interlinking the VIA        columns and the VIA rows;    -   the VIA is configured to electrically couple a plurality of        interlinked impedance columns (IIC) within the TSA with a        plurality of interlinked impedance rows (IIR) within the TSA;    -   the IIC further comprises a plurality of individual column        impedance elements (ICIE) electrically connected in series        between the VIA columns;    -   the IIR further comprises a plurality of individual row        impedance elements (IRIE) electrically connected in series        between the VIA rows;    -   the ACD is configured to select the IIC within the TSA based on        the CSR;    -   the ACD is configured to electrically drive the selected IIC        using the CDS;    -   the ARS is configured to select the IIR within the TSA based on        the RSR;    -   the ADC is configured to sense the electrical state of the        selected IIR and convert the electrical state to a sensed        digital value (SDV);    -   the electrical state is determined by the sum of current        contributions of variable impedance elements within the VIA,        where the current contribution of each element is determined by        a voltage divider formed between the columns of the VIA, a        current divider formed between the rows of the via, and the        state of the impedance element, to produce a sensed current for        a given row-column intersection with the VIA; and    -   the CCD is configured to sample the SDV from the ADC at a        plurality of positions within the TSA to form a touch sensor        matrix (TSM) data structure;

wherein the method comprises the steps of:

-   -   (1) under control of the CCD, configuring the IIC within the        VIA;    -   (1) under control of the CCD, configuring the IIR within the        VIA;    -   (2) under control of the CCD, electrically stimulating the IIC        with the CDS;    -   (3) under control of the CCD, sensing the electrical state in        the IIR with the ADC as a sensed current for a given row-column        intersection within the VIA and converting the electrical state        to digital data;    -   (4) under control of the CCD, storing the digital data in the        TSM;    -   (5) under control of the CCD, determining if predetermined        variations in the CDR, the IIC, and the IIR have been logged to        the TSM, and if so, proceeding to step (8);    -   (6) under control of the CCD, reconfiguring the CDS, the IIC,        and the IIR for a new VIA sensing variant and proceeding to step        (3);    -   (7) under control of the CCD, interpolating the TSM values to        determine focal points of activity within the VIA;    -   (8) under control of the CCD, converting the focal point        activity information into a user interface input command        sequence; and    -   (9) under control of the CCD, transmitting the user interface        input command sequence to a computer system for action and        proceeding to step (1).

This general method summary may be augmented by the various elementsdescribed herein to produce a wide variety of invention embodimentsconsistent with this overall design description.

System/Method Variations

The present invention anticipates a wide variety of variations in thebasic theme of construction. The examples presented previously do notrepresent the entire scope of possible usages. They are meant to cite afew of the almost limitless possibilities.

This basic system and method may be augmented with a variety ofancillary embodiments, including but not limited to:

-   -   An embodiment wherein the VIA further comprises a force sensing        material responsive to pressure applied to the TSA and wherein        the CCD is configured to determine pressure applied to the TSA        by measurement of resistances in the VIA.    -   An embodiment wherein the CCD is configured to combine        capacitive and force sensing data from the TSA to form an        average touch sensing value associated with the TSA.    -   An embodiment wherein the CCD is configured to combine        capacitive sensing data and force sensing data from the TSA        using a weighted average to form a combined touch sensing value        associated with the TSA.    -   An embodiment wherein the CCD is configured to combine        capacitive sensing data and force sensing data from the TSA        using a weighted average to form a combined touch sensing value        associated with the TSA where the capacitance associated with        the capacitance sensing data is weighted more than the force        associated with the force sensing data.    -   An embodiment wherein the CCD is configured to combine        capacitive sensing data and force sensing data from the TSA        using a weighted average to form a combined touch sensing value        associated with the TSA where the force associated with the        force sensing data is weighted more than the capacitive        associated with the capacitive sensing data.    -   An embodiment wherein the CCD is configured to scan the VIA        using a mutual-capacitance scan which determines the presence of        a touch at each row/column intersection within the VIA.    -   An embodiment wherein the CCD is configured to scan the VIA        using a self-capacitance scan which determines the presence of a        touch either at a given row within the VIA or at a given column        within the VIA.    -   An embodiment wherein the CCD is configured to scan the VIA with        a subset of active electrodes in the VIA configured in a high        impedance state.    -   An embodiment wherein the VIA comprises sensing elements that        change capacitance in response to force applied to the TSA.    -   An embodiment wherein the CCD is configured to collect both        capacitive sensing data (CSD) and force sensing data (FSD) from        the TSA and store the CSD and the FSD in the TSM.    -   An embodiment wherein the CCD is configured to collect        capacitive sensing data (CSD) and force sensing data (FSD)        associated with an active stylus from the TSA and store the CSD        and the FSD in the TSM.    -   An embodiment wherein the ACD comprises a digital-to-analog        converter (DAC) configured to generate a sine wave.    -   An embodiment wherein the ADC comprises an analog-to-digital        converter configured to detect a sine wave.    -   An embodiment wherein the CCD comprises a state machine        configured to determine if the SDV constitutes a touch state        derived from a conductive object or a non-conductive object.    -   An embodiment wherein the ACD comprises a single transmitter        configured to scan the VIA one active row-column intersection at        a time with the ARS comprising a receiver configured to sense a        single row of the VIA at a time.    -   An embodiment wherein the ACD comprises multiple transmitters        configured to drive multiple columns of the VIA.    -   An embodiment wherein the ARS comprises multiple receivers        configured to sense multiple rows of the VIA.    -   An embodiment wherein the ACD comprises multiple transmitters        operating at multiple frequencies configured to drive multiple        columns of the VIA.    -   An embodiment wherein the ACD comprises multiple transmitters        operating at multiple frequencies configured to drive multiple        columns of the VIA and the ARS comprises multiple receivers        configured to sense multiple rows of the VIA at multiple        frequencies.    -   An embodiment wherein the VIA comprises drive electrodes and        sense electrodes placed on the same layer and conductive bridges        allowing one set of the drive electrodes and the sense        electrodes to overlap the other without shorting.    -   An embodiment wherein the VIA comprises a diamond pattern with        drive electrodes and sense electrodes placed on the same layer        and conductive bridges allowing one set of the drive electrodes        and the sense electrodes to overlap the other without shorting.    -   An embodiment wherein the VIA comprises a two layer structure        incorporating the IIC and the IIR.    -   An embodiment wherein the VIA comprises sensor elements having a        row-column pitch in the range of 0.25 to 2.5 mm.    -   An embodiment wherein the VIA comprises a resistive sensor        element.    -   An embodiment wherein the VIA comprises sensor elements        comprising an inductor.    -   An embodiment wherein the VIA comprises sensor elements        comprising any combination of resistor, capacitor, and inductor.    -   An embodiment wherein the ICIE comprises a printed narrow        resistive strip.    -   An embodiment wherein the IRIE comprises a printed narrow        resistive strip.    -   An embodiment wherein the ICIE comprises a thin bridge of        transparent conductive material.    -   An embodiment wherein the IRIE comprises a thin bridge of        transparent conductive material.    -   An embodiment wherein the ICIE and the IRIE are comprised of the        same material as respective columns and rows of the VIA.    -   An embodiment wherein the ICIE and the IRIE are comprised of        laser trimmed resistors.    -   An embodiment wherein the VIA is covered with a thin dielectric        layer.    -   An embodiment wherein the TSA further comprises a display        separated from the VIA by a transparent conductive layer of        shielding material.    -   An embodiment wherein the VIA further comprises column        electrodes and row electrodes formed from a transparent        conductive material.    -   An embodiment wherein the VIA further comprises column        electrodes and row electrodes formed from a transparent        conductive material selected from a group consisting of: indium        tin oxide (ITO); transparent organic conductive particles;        graphene; carbon nanotubes; silver nanowires; micro-patterned        conductive mesh; transparent conductive polymer; and metal        nanoparticles.    -   An embodiment wherein the VIA is formed on the top of or        laminated to a display.    -   An embodiment wherein the VIA is integrated within the layers of        a display.    -   An embodiment wherein the TSA is configured to transmit a signal        to a stylus from each row and column in the VIA and the stylus        is configured to determine a signal strength from the        transmission and transmit the signal strength to the CCD.    -   An embodiment wherein the TSA is configured to receive a signal        from a stylus from each row and column in the VIA and determine        the location of the stylus by analysis of the received signal.    -   An embodiment wherein the TSA is configured to determine the        position of a stylus by bi-directionally communicating with the        stylus via rows and columns of the VIA.    -   An embodiment wherein the TSA is configured to communicate with        multiple styli via the rows and columns of the VIA.    -   An embodiment wherein the TSA is configured to communicate with        a stylus having multiple transceivers.    -   An embodiment wherein the TSA is configured to communicate with        a stylus configured to communicate with a host computer via        BLUETOOTH® wireless communication.

One skilled in the art will recognize that other embodiments arepossible based on combinations of elements taught within the aboveinvention description.

Generalized Computer Usable Medium

In various alternate embodiments, the present invention may beimplemented as a computer program product for use with a computerizedcomputing system. Those skilled in the art will readily appreciate thatprograms defining the functions defined by the present invention can bewritten in any appropriate programming language and delivered to acomputer in many forms, including but not limited to: (a) informationpermanently stored on non-writeable storage media (e.g., read-onlymemory devices such as ROMs or CD-ROM disks); (b) information alterablystored on writeable storage media (e.g., floppy disks and hard drives);and/or (c) information conveyed to a computer through communicationmedia, such as a local area network, a telephone network, or a publicnetwork such as the Internet. When carrying computer readableinstructions that implement the present invention methods, such computerreadable media represent alternate embodiments of the present invention.

As generally illustrated herein, the present invention systemembodiments can incorporate a variety of computer readable media thatcomprise computer usable medium having computer readable code meansembodied therein. One skilled in the art will recognize that thesoftware associated with the various processes described herein can beembodied in a wide variety of computer accessible media from which thesoftware is loaded and activated. Pursuant to In re Beauregard, 35USPQ2d 1383 (U.S. Pat. No. 5,710,578), the present invention anticipatesand includes this type of computer readable media within the scope ofthe invention. Pursuant to In re Nuijten, 500 F.3d 1346 (Fed. Cir. 2007)(U.S. patent application Ser. No. 09/211,928), the present inventionscope is limited to computer readable media wherein the media is bothtangible and non-transitory.

CONCLUSION

A touch sensor detector system and method incorporating an interpolatedsensor array has been disclosed. The system and method utilize a touchsensor array (TSA) configured to detect proximity/contact/pressure (PCP)via a variable impedance array (VIA) electrically coupling interlinkedimpedance columns (IIC) coupled to an array column driver (ACD), andinterlinked impedance rows (IIR) coupled to an array row sensor (ARS).The ACD is configured to select the IIC based on a column switchingregister (CSR) and electrically drive the IIC using a column drivingsource (CDS). The VIA conveys current from the driven IIC to the IICsensed by the ARS. The ARS selects the IIR within the TSA andelectrically senses the IIR state based on a row switching register(RSR). Interpolation of ARS sensed current/voltage allows accuratedetection of TSA PCP and/or spatial location.

CLAIMS INTERPRETATION

The following rules apply when interpreting the CLAIMS of the presentinvention:

-   -   The CLAIM PREAMBLE should be considered as limiting the scope of        the claimed invention.    -   “WHEREIN” clauses should be considered as limiting the scope of        the claimed invention.    -   “WHEREBY” clauses should be considered as limiting the scope of        the claimed invention.    -   “ADAPTED TO” clauses should be considered as limiting the scope        of the claimed invention.    -   “ADAPTED FOR” clauses should be considered as limiting the scope        of the claimed invention.    -   The term “MEANS” specifically invokes the means-plus-function        claims limitation recited in 35 U.S.C. § 112(f) and such claim        shall be construed to cover the corresponding structure,        material, or acts described in the specification and equivalents        thereof.    -   The phrase “MEANS FOR” specifically invokes the        means-plus-function claims limitation recited in 35 U.S.C. §        112(f) and such claim shall be construed to cover the        corresponding structure, material, or acts described in the        specification and equivalents thereof.    -   The phrase “STEP FOR” specifically invokes the        step-plus-function claims limitation recited in 35 U.S.C. §        112(f) and such claim shall be construed to cover the        corresponding structure, material, or acts described in the        specification and equivalents thereof.    -   The step-plus-function claims limitation recited in 35 U.S.C. §        112(f) shall be construed to cover the corresponding structure,        material, or acts described in the specification and equivalents        thereof ONLY for such claims including the phrases “MEANS FOR”,        “MEANS”, or “STEP FOR”.    -   The phrase “AND/OR” in the context of an expression “X and/or Y”        should be interpreted to define the set of “(X and Y)” in union        with the set “(X or Y)” as interpreted by Ex Parte Gross (USPTO        Patent Trial and Appeal Board, Appeal 2011-004811, Ser. No.        11/565,411, (“‘and/or’ covers embodiments having element A        alone, B alone, or elements A and B taken together”).    -   The claims presented herein are to be interpreted in light of        the specification and drawings presented herein with        sufficiently narrow scope such as to not preempt any abstract        idea.    -   The claims presented herein are to be interpreted in light of        the specification and drawings presented herein with        sufficiently narrow scope such as to not preclude every        application of any idea.    -   The claims presented herein are to be interpreted in light of        the specification and drawings presented herein with        sufficiently narrow scope such as to preclude any basic mental        process that could be performed entirely in the human mind.    -   The claims presented herein are to be interpreted in light of        the specification and drawings presented herein with        sufficiently narrow scope such as to preclude any process that        could be performed entirely by human manual effort.

What is claimed is:
 1. A sensor, comprising: a sensing area comprising agrid of force sensing elements, where force sensing elements of the gridof force sensing elements are connected between respective rowelectrodes of a group of row electrodes and respective column electrodesof a group of column electrodes; an AC signal source operativelyconnected between column multiplexing circuitry and a control circuit;and an analog switch operatively connected between the control circuitand the sensing area, wherein the analog switch facilitates alternating,for respective force sensing elements being scanned, between a firstscan of the sensing area via the AC signal source and a second scan ofthe sensing area via a DC voltage source.
 2. The sensor of claim 1,wherein the alternating between the first scan and the second scan isperformed on a per-scan basis.
 3. The sensor of claim 1, wherein thefirst scan is based on: the DC voltage source being disabled; andreceipt of a signal from an AC signal detector.
 4. The sensor of claim1, wherein the second scan is based on: the AC signal source beingdisabled; and receipt of a signal from a DC signal conditioning circuit.5. The sensor of claim 1, wherein the first scan via the AC signalsource measures capacitive coupling caused by a force applied to thesensing area.
 6. The sensor of claim 1, wherein the second scan via theDC voltage source measures a force applied to the sensing area.
 7. Thesensor of claim 1, further comprising: an AC signal detector thatconverts an AC signal received from the AC signal source into a DCvoltage level enabled to be read by an analog to digital converter. 8.The sensor of claim 1, wherein a first position of the analog switchfacilitates the first scan of the sensing area via an AC signal providedby the AC signal source, and wherein a second position of the analogswitch facilitates the second scan of the sensing area via a DC voltageprovided by the DC voltage source.
 9. The sensor of claim 1, wherein thecolumn multiplexing circuitry facilitates electrical grounding ofcolumns not being actively driven.
 10. The sensor of claim 1, whereinthe DC voltage source is operatively connected between the controlcircuit and the sensing area.
 11. The sensor of claim 10, wherein a DCvoltage level indicates a strength of a received AC signal.
 12. Thesensor of claim 1, wherein the sensor is a touch sensor.
 13. The sensorof claim 1, wherein the sensor is a force-sensing sensor.